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/pretty-formats.txt

@@ -4,7 +4,7 @@ PRETTY FORMATS
 If the commit is a merge, and if the pretty-format
 is not 'oneline', 'email' or 'raw', an additional line is
 inserted before the 'Author:' line.  This line begins with
-"Merge: " and the sha1s of ancestral commits are printed,
+"Merge: " and the hashes of ancestral commits are printed,
 separated by spaces.  Note that the listed commits may not
 necessarily be the list of the *direct* parent commits if you
 have limited your view of history: for example, if you are
@@ -20,20 +20,20 @@ built-in formats:
 
 * 'oneline'
 
-	  <sha1> <title line>
+	  <hash> <title line>
 +
 This is designed to be as compact as possible.
 
 * 'short'
 
-	  commit <sha1>
+	  commit <hash>
 	  Author: <author>
 
 	      <title line>
 
 * 'medium'
 
-	  commit <sha1>
+	  commit <hash>
 	  Author: <author>
 	  Date:   <author date>
 
@@ -43,7 +43,7 @@ This is designed to be as compact as possible.
 
 * 'full'
 
-	  commit <sha1>
+	  commit <hash>
 	  Author: <author>
 	  Commit: <committer>
 
@@ -53,7 +53,7 @@ This is designed to be as compact as possible.
 
 * 'fuller'
 
-	  commit <sha1>
+	  commit <hash>
 	  Author:     <author>
 	  AuthorDate: <author date>
 	  Commit:     <committer>
@@ -63,19 +63,36 @@ This is designed to be as compact as possible.
 
 	       <full commit message>
 
+* 'reference'
+
+	  <abbrev hash> (<title line>, <short author date>)
++
+This format is used to refer to another commit in a commit message and
+is the same as `--pretty='format:%C(auto)%h (%s, %ad)'`.  By default,
+the date is formatted with `--date=short` unless another `--date` option
+is explicitly specified.  As with any `format:` with format
+placeholders, its output is not affected by other options like
+`--decorate` and `--walk-reflogs`.
+
 * 'email'
 
-	  From <sha1> <date>
+	  From <hash> <date>
 	  From: <author>
 	  Date: <author date>
 	  Subject: [PATCH] <title line>
 
 	  <full commit message>
 
+* 'mboxrd'
++
+Like 'email', but lines in the commit message starting with "From "
+(preceded by zero or more ">") are quoted with ">" so they aren't
+confused as starting a new commit.
+
 * 'raw'
 +
 The 'raw' format shows the entire commit exactly as
-stored in the commit object.  Notably, the SHA-1s are
+stored in the commit object.  Notably, the hashes are
 displayed in full, regardless of whether --abbrev or
 --no-abbrev are used, and 'parents' information show the
 true parent commits, without taking grafts or history
@@ -163,24 +180,32 @@ The placeholders are:
 '%ae':: author email
 '%aE':: author email (respecting .mailmap, see linkgit:git-shortlog[1]
 	or linkgit:git-blame[1])
+'%al':: author email local-part (the part before the '@' sign)
+'%aL':: author local-part (see '%al') respecting .mailmap, see
+	linkgit:git-shortlog[1] or linkgit:git-blame[1])
 '%ad':: author date (format respects --date= option)
 '%aD':: author date, RFC2822 style
 '%ar':: author date, relative
 '%at':: author date, UNIX timestamp
 '%ai':: author date, ISO 8601-like format
 '%aI':: author date, strict ISO 8601 format
+'%as':: author date, short format (`YYYY-MM-DD`)
 '%cn':: committer name
 '%cN':: committer name (respecting .mailmap, see
 	linkgit:git-shortlog[1] or linkgit:git-blame[1])
 '%ce':: committer email
 '%cE':: committer email (respecting .mailmap, see
 	linkgit:git-shortlog[1] or linkgit:git-blame[1])
+'%cl':: committer email local-part (the part before the '@' sign)
+'%cL':: committer local-part (see '%cl') respecting .mailmap, see
+	linkgit:git-shortlog[1] or linkgit:git-blame[1])
 '%cd':: committer date (format respects --date= option)
 '%cD':: committer date, RFC2822 style
 '%cr':: committer date, relative
 '%ct':: committer date, UNIX timestamp
 '%ci':: committer date, ISO 8601-like format
 '%cI':: committer date, strict ISO 8601 format
+'%cs':: committer date, short format (`YYYY-MM-DD`)
 '%d':: ref names, like the --decorate option of linkgit:git-log[1]
 '%D':: ref names without the " (", ")" wrapping.
 '%S':: ref name given on the command line by which the commit was reached
@@ -207,8 +232,9 @@ endif::git-rev-list[]
 '%GF':: show the fingerprint of the key used to sign a signed commit
 '%GP':: show the fingerprint of the primary key whose subkey was used
 	to sign a signed commit
+'%GT':: show the trust level for the key used to sign a signed commit
 '%gD':: reflog selector, e.g., `refs/stash@{1}` or `refs/stash@{2
-	minutes ago`}; the format follows the rules described for the
+	minutes ago}`; the format follows the rules described for the
 	`-g` option. The portion before the `@` is the refname as
 	given on the command line (so `git log -g refs/heads/master`
 	would yield `refs/heads/master@{0}`).