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/config/core.txt

@@ -68,6 +68,17 @@ core.fsmonitor::
 	avoiding unnecessary processing of files that have not changed.
 	See the "fsmonitor-watchman" section of linkgit:githooks[5].
 
+core.fsmonitorHookVersion::
+	Sets the version of hook that is to be used when calling fsmonitor.
+	There are currently versions 1 and 2. When this is not set,
+	version 2 will be tried first and if it fails then version 1
+	will be tried. Version 1 uses a timestamp as input to determine
+	which files have changes since that time but some monitors
+	like watchman have race conditions when used with a timestamp.
+	Version 2 uses an opaque string so that the monitor can return
+	something that can be used to determine what files have changed
+	without race conditions.
+
 core.trustctime::
 	If false, the ctime differences between the index and the
 	working tree are ignored; useful when the inode change time
@@ -86,7 +97,9 @@ core.untrackedCache::
 	it will automatically be removed, if set to `false`. Before
 	setting it to `true`, you should check that mtime is working
 	properly on your system.
-	See linkgit:git-update-index[1]. `keep` by default.
+	See linkgit:git-update-index[1]. `keep` by default, unless
+	`feature.manyFiles` is enabled which sets this setting to
+	`true` by default.
 
 core.checkStat::
 	When missing or is set to `default`, many fields in the stat
@@ -386,7 +399,7 @@ the largest projects.  You probably do not need to adjust this value.
 Common unit suffixes of 'k', 'm', or 'g' are supported.
 
 core.deltaBaseCacheLimit::
-	Maximum number of bytes to reserve for caching base objects
+	Maximum number of bytes per thread to reserve for caching base objects
 	that may be referenced by multiple deltified objects.  By storing the
 	entire decompressed base objects in a cache Git is able
 	to avoid unpacking and decompressing frequently used base
@@ -557,6 +570,12 @@ core.unsetenvvars::
 	Defaults to `PERL5LIB` to account for the fact that Git for
 	Windows insists on using its own Perl interpreter.
 
+core.restrictinheritedhandles::
+	Windows-only: override whether spawned processes inherit only standard
+	file handles (`stdin`, `stdout` and `stderr`) or all handles. Can be
+	`auto`, `true` or `false`. Defaults to `auto`, which means `true` on
+	Windows 7 and later, and `false` on older Windows versions.
+
 core.createObject::
 	You can set this to 'link', in which case a hardlink followed by
 	a delete of the source are used to make sure that object creation
@@ -577,7 +596,7 @@ the `GIT_NOTES_REF` environment variable.  See linkgit:git-notes[1].
 
 core.commitGraph::
 	If true, then git will read the commit-graph file (if it exists)
-	to parse the graph structure of commits. Defaults to false. See
+	to parse the graph structure of commits. Defaults to true. See
 	linkgit:git-commit-graph[1] for more information.
 
 core.useReplaceRefs::
@@ -591,8 +610,14 @@ core.multiPackIndex::
 	multi-pack-index design document].
 
 core.sparseCheckout::
-	Enable "sparse checkout" feature. See section "Sparse checkout" in
-	linkgit:git-read-tree[1] for more information.
+	Enable "sparse checkout" feature. See linkgit:git-sparse-checkout[1]
+	for more information.
+
+core.sparseCheckoutCone::
+	Enables the "cone mode" of the sparse checkout feature. When the
+	sparse-checkout file contains a limited set of patterns, then this
+	mode provides significant performance advantages. See
+	linkgit:git-sparse-checkout[1] for more information.
 
 core.abbrev::
 	Set the length object names are abbreviated to.  If