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-status.txt

@@ -59,16 +59,17 @@ This is optional and defaults to the original version 'v1' format.
 --untracked-files[=<mode>]::
 	Show untracked files.
 +
+--
 The mode parameter is used to specify the handling of untracked files.
 It is optional: it defaults to 'all', and if specified, it must be
 stuck to the option (e.g. `-uno`, but not `-u no`).
-+
+
 The possible options are:
-+
+
 	- 'no'     - Show no untracked files.
 	- 'normal' - Shows untracked files and directories.
 	- 'all'    - Also shows individual files in untracked directories.
-+
+
 When `-u` option is not used, untracked files and directories are
 shown (i.e. the same as specifying `normal`), to help you avoid
 forgetting to add newly created files.  Because it takes extra work
@@ -78,9 +79,10 @@ Consider enabling untracked cache and split index if supported (see
 `git update-index --untracked-cache` and `git update-index
 --split-index`), Otherwise you can use `no` to have `git status`
 return more quickly without showing untracked files.
-+
+
 The default can be changed using the status.showUntrackedFiles
 configuration variable documented in linkgit:git-config[1].
+--
 
 --ignore-submodules[=<when>]::
 	Ignore changes to submodules when looking for changes. <when> can be
@@ -100,11 +102,12 @@ configuration variable documented in linkgit:git-config[1].
 --ignored[=<mode>]::
 	Show ignored files as well.
 +
+--
 The mode parameter is used to specify the handling of ignored files.
 It is optional: it defaults to 'traditional'.
-+
+
 The possible options are:
-+
+
 	- 'traditional' - Shows ignored files and directories, unless
 			  --untracked-files=all is specified, in which case
 			  individual files in ignored directories are
@@ -112,12 +115,13 @@ The possible options are:
 	- 'no'	        - Show no ignored files.
 	- 'matching'    - Shows ignored files and directories matching an
 			  ignore pattern.
-+
+
 When 'matching' mode is specified, paths that explicitly match an
 ignored pattern are shown. If a directory matches an ignore pattern,
 then it is shown, but not paths contained in the ignored directory. If
 a directory does not match an ignore pattern, but all contents are
 ignored, then the directory is not shown, but all contents are shown.
+--
 
 -z::
 	Terminate entries with NUL, instead of LF.  This implies