merge(3p/git): Merge git subtree at v2.29.2

This also bumps the stable nixpkgs to 20.09 as of 2020-11-21, because
there is some breakage in the git build related to the netrc
credentials helper which someone has taken care of in nixpkgs.

The stable channel is not used for anything other than git, so this
should be fine.

Change-Id: I3575a19dab09e1e9556cf8231d717de9890484fb

third_party/git/Documentation/git.txt

@@ -110,9 +110,23 @@ foo.bar= ...`) sets `foo.bar` to the empty string which `git config
 	Do not pipe Git output into a pager.
 
 --git-dir=<path>::
-	Set the path to the repository. This can also be controlled by
-	setting the `GIT_DIR` environment variable. It can be an absolute
-	path or relative path to current working directory.
+	Set the path to the repository (".git" directory). This can also be
+	controlled by setting the `GIT_DIR` environment variable. It can be
+	an absolute path or relative path to current working directory.
++
+Specifying the location of the ".git" directory using this
+option (or `GIT_DIR` environment variable) turns off the
+repository discovery that tries to find a directory with
+".git" subdirectory (which is how the repository and the
+top-level of the working tree are discovered), and tells Git
+that you are at the top level of the working tree.  If you
+are not at the top-level directory of the working tree, you
+should tell Git where the top-level of the working tree is,
+with the `--work-tree=<path>` option (or `GIT_WORK_TREE`
+environment variable)
++
+If you just want to run git as if it was started in `<path>` then use
+`git -C <path>`.
 
 --work-tree=<path>::
 	Set the path to the working tree. It can be an absolute path
@@ -271,8 +285,8 @@ In general, the interrogate commands do not touch the files in
 the working tree.
 
 
-Synching repositories
-~~~~~~~~~~~~~~~~~~~~~
+Syncing repositories
+~~~~~~~~~~~~~~~~~~~~
 
 include::cmds-synchingrepositories.txt[]
 
@@ -290,6 +304,13 @@ users typically do not use them directly.
 
 include::cmds-purehelpers.txt[]
 
+Guides
+------
+
+The following documentation pages are guides about Git concepts.
+
+include::cmds-guide.txt[]
+
 
 Configuration Mechanism
 -----------------------
@@ -479,16 +500,46 @@ double-quotes and respecting backslash escapes. E.g., the value
 	details. This variable has lower precedence than other path
 	variables such as GIT_INDEX_FILE, GIT_OBJECT_DIRECTORY...
 
+`GIT_DEFAULT_HASH`::
+	If this variable is set, the default hash algorithm for new
+	repositories will be set to this value. This value is currently
+	ignored when cloning; the setting of the remote repository
+	is used instead. The default is "sha1". THIS VARIABLE IS
+	EXPERIMENTAL! See `--object-format` in linkgit:git-init[1].
+
 Git Commits
 ~~~~~~~~~~~
 `GIT_AUTHOR_NAME`::
+	The human-readable name used in the author identity when creating commit or
+	tag objects, or when writing reflogs. Overrides the `user.name` and
+	`author.name` configuration settings.
+
 `GIT_AUTHOR_EMAIL`::
+	The email address used in the author identity when creating commit or
+	tag objects, or when writing reflogs. Overrides the `user.email` and
+	`author.email` configuration settings.
+
 `GIT_AUTHOR_DATE`::
+	The date used for the author identity when creating commit or tag objects, or
+	when writing reflogs. See linkgit:git-commit[1] for valid formats.
+
 `GIT_COMMITTER_NAME`::
+	The human-readable name used in the committer identity when creating commit or
+	tag objects, or when writing reflogs. Overrides the `user.name` and
+	`committer.name` configuration settings.
+
 `GIT_COMMITTER_EMAIL`::
+	The email address used in the author identity when creating commit or
+	tag objects, or when writing reflogs. Overrides the `user.email` and
+	`committer.email` configuration settings.
+
 `GIT_COMMITTER_DATE`::
-'EMAIL'::
-	see linkgit:git-commit-tree[1]
+	The date used for the committer identity when creating commit or tag objects, or
+	when writing reflogs. See linkgit:git-commit[1] for valid formats.
+
+`EMAIL`::
+	The email address used in the author and committer identities if no other
+	relevant environment variable or configuration setting has been set.
 
 Git Diffs
 ~~~~~~~~~
@@ -500,8 +551,9 @@ Git Diffs
 
 `GIT_EXTERNAL_DIFF`::
 	When the environment variable `GIT_EXTERNAL_DIFF` is set, the
-	program named by it is called, instead of the diff invocation
-	described above.  For a path that is added, removed, or modified,
+	program named by it is called to generate diffs, and Git
+	does not use its builtin diff machinery.
+	For a path that is added, removed, or modified,
 	`GIT_EXTERNAL_DIFF` is called with 7 parameters:
 
 	path old-file old-hex old-mode new-file new-hex new-mode
@@ -544,12 +596,22 @@ other
 	a pager.  See also the `core.pager` option in
 	linkgit:git-config[1].
 
+`GIT_PROGRESS_DELAY`::
+	A number controlling how many seconds to delay before showing
+	optional progress indicators. Defaults to 2.
+
 `GIT_EDITOR`::
 	This environment variable overrides `$EDITOR` and `$VISUAL`.
 	It is used by several Git commands when, on interactive mode,
 	an editor is to be launched. See also linkgit:git-var[1]
 	and the `core.editor` option in linkgit:git-config[1].
 
+`GIT_SEQUENCE_EDITOR`::
+	This environment variable overrides the configured Git editor
+	when editing the todo list of an interactive rebase. See also
+	linkit::git-rebase[1] and the `sequence.editor` option in
+	linkit::git-config[1].
+
 `GIT_SSH`::
 `GIT_SSH_COMMAND`::
 	If either of these environment variables is set then 'git fetch'
@@ -660,6 +722,10 @@ of clones and fetches.
 	time of each Git command.
 	See `GIT_TRACE` for available trace output options.
 
+`GIT_TRACE_REFS`::
+	Enables trace messages for operations on the ref database.
+	See `GIT_TRACE` for available trace output options.
+
 `GIT_TRACE_SETUP`::
 	Enables trace messages printing the .git, working tree and current
 	working directory after Git has completed its setup phase.
@@ -674,8 +740,6 @@ of clones and fetches.
 	Enables a curl full trace dump of all incoming and outgoing data,
 	including descriptive information, of the git transport protocol.
 	This is similar to doing curl `--trace-ascii` on the command line.
-	This option overrides setting the `GIT_CURL_VERBOSE` environment
-	variable.
 	See `GIT_TRACE` for available trace output options.
 
 `GIT_TRACE_CURL_NO_DATA`::
@@ -730,11 +794,10 @@ for full details.
 	See `GIT_TRACE2` for available trace output options and
 	link:technical/api-trace2.html[Trace2 documentation] for full details.
 
-`GIT_REDACT_COOKIES`::
-	This can be set to a comma-separated list of strings. When a curl trace
-	is enabled (see `GIT_TRACE_CURL` above), whenever a "Cookies:" header
-	sent by the client is dumped, values of cookies whose key is in that
-	list (case-sensitive) are redacted.
+`GIT_TRACE_REDACT`::
+	By default, when tracing is activated, Git redacts the values of
+	cookies, the "Authorization:" header, and the "Proxy-Authorization:"
+	header. Set this variable to `0` to prevent this redaction.
 
 `GIT_LITERAL_PATHSPECS`::
 	Setting this variable to `1` will cause Git to treat all
@@ -928,7 +991,7 @@ Reporting Bugs
 Report bugs to the Git mailing list <git@vger.kernel.org> where the
 development and maintenance is primarily done.  You do not have to be
 subscribed to the list to send a message there.  See the list archive
-at https://public-inbox.org/git for previous bug reports and other
+at https://lore.kernel.org/git for previous bug reports and other
 discussions.
 
 Issues which are security relevant should be disclosed privately to