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-commit.txt

@@ -13,7 +13,8 @@ SYNOPSIS
 	   [-F <file> | -m <msg>] [--reset-author] [--allow-empty]
 	   [--allow-empty-message] [--no-verify] [-e] [--author=<author>]
 	   [--date=<date>] [--cleanup=<mode>] [--[no-]status]
-	   [-i | -o] [-S[<keyid>]] [--] [<file>...]
+	   [-i | -o] [--pathspec-from-file=<file> [--pathspec-file-nul]]
+	   [-S[<keyid>]] [--] [<pathspec>...]
 
 DESCRIPTION
 -----------
@@ -278,22 +279,37 @@ FROM UPSTREAM REBASE" section in linkgit:git-rebase[1].)
 	already been staged. If used together with `--allow-empty`
 	paths are also not required, and an empty commit will be created.
 
+--pathspec-from-file=<file>::
+	Pathspec is passed in `<file>` instead of commandline args. If
+	`<file>` is exactly `-` then standard input is used. Pathspec
+	elements are separated by LF or CR/LF. Pathspec elements can be
+	quoted as explained for the configuration variable `core.quotePath`
+	(see linkgit:git-config[1]). See also `--pathspec-file-nul` and
+	global `--literal-pathspecs`.
+
+--pathspec-file-nul::
+	Only meaningful with `--pathspec-from-file`. Pathspec elements are
+	separated with NUL character and all other characters are taken
+	literally (including newlines and quotes).
+
 -u[<mode>]::
 --untracked-files[=<mode>]::
 	Show untracked files.
 +
+--
 The mode parameter is optional (defaults to 'all'), and is used to
 specify the handling of untracked files; when -u is not used, the
 default is 'normal', i.e. show untracked files and directories.
-+
+
 The possible options are:
-+
+
 	- 'no'     - Show no untracked files
 	- 'normal' - Shows untracked files and directories
 	- 'all'    - Also shows individual files in untracked directories.
-+
+
 The default can be changed using the status.showUntrackedFiles
 configuration variable documented in linkgit:git-config[1].
+--
 
 -v::
 --verbose::
@@ -332,26 +348,23 @@ changes to tracked files.
 
 -S[<keyid>]::
 --gpg-sign[=<keyid>]::
+--no-gpg-sign::
 	GPG-sign commits. The `keyid` argument is optional and
 	defaults to the committer identity; if specified, it must be
-	stuck to the option without a space.
-
---no-gpg-sign::
-	Countermand `commit.gpgSign` configuration variable that is
-	set to force each and every commit to be signed.
+	stuck to the option without a space. `--no-gpg-sign` is useful to
+	countermand both `commit.gpgSign` configuration variable, and
+	earlier `--gpg-sign`.
 
 \--::
 	Do not interpret any more arguments as options.
 
-<file>...::
-	When files are given on the command line, the command
-	commits the contents of the named files, without
-	recording the changes already staged.  The contents of
-	these files are also staged for the next commit on top
-	of what have been staged before.
-
-:git-commit: 1
-include::date-formats.txt[]
+<pathspec>...::
+	When pathspec is given on the command line, commit the contents of
+	the files that match the pathspec without recording the changes
+	already added to the index. The contents of these files are also
+	staged for the next commit on top of what have been staged before.
++
+For more details, see the 'pathspec' entry in linkgit:gitglossary[7].
 
 EXAMPLES
 --------
@@ -446,6 +459,43 @@ alter the order the changes are committed, because the merge
 should be recorded as a single commit.  In fact, the command
 refuses to run when given pathnames (but see `-i` option).
 
+COMMIT INFORMATION
+------------------
+
+Author and committer information is taken from the following environment
+variables, if set:
+
+	GIT_AUTHOR_NAME
+	GIT_AUTHOR_EMAIL
+	GIT_AUTHOR_DATE
+	GIT_COMMITTER_NAME
+	GIT_COMMITTER_EMAIL
+	GIT_COMMITTER_DATE
+
+(nb "<", ">" and "\n"s are stripped)
+
+The author and committer names are by convention some form of a personal name
+(that is, the name by which other humans refer to you), although Git does not
+enforce or require any particular form. Arbitrary Unicode may be used, subject
+to the constraints listed above. This name has no effect on authentication; for
+that, see the `credential.username` variable in linkgit:git-config[1].
+
+In case (some of) these environment variables are not set, the information
+is taken from the configuration items `user.name` and `user.email`, or, if not
+present, the environment variable EMAIL, or, if that is not set,
+system user name and the hostname used for outgoing mail (taken
+from `/etc/mailname` and falling back to the fully qualified hostname when
+that file does not exist).
+
+The `author.name` and `committer.name` and their corresponding email options
+override `user.name` and `user.email` if set and are overridden themselves by
+the environment variables.
+
+The typical usage is to set just the `user.name` and `user.email` variables;
+the other options are provided for more complex use cases.
+
+:git-commit: 1
+include::date-formats.txt[]
 
 DISCUSSION
 ----------