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/format.txt

@@ -36,6 +36,12 @@ format.subjectPrefix::
 	The default for format-patch is to output files with the '[PATCH]'
 	subject prefix. Use this variable to change that prefix.
 
+format.coverFromDescription::
+	The default mode for format-patch to determine which parts of
+	the cover letter will be populated using the branch's
+	description. See the `--cover-from-description` option in
+	linkgit:git-format-patch[1].
+
 format.signature::
 	The default for format-patch is to output a signature containing
 	the Git version number. Use this variable to change that default.
@@ -51,6 +57,11 @@ format.suffix::
 	`.patch`. Use this variable to change that suffix (make sure to
 	include the dot if you want it).
 
+format.encodeEmailHeaders::
+	Encode email headers that have non-ASCII characters with
+	"Q-encoding" (described in RFC 2047) for email transmission.
+	Defaults to true.
+
 format.pretty::
 	The default pretty format for log/show/whatchanged command,
 	See linkgit:git-log[1], linkgit:git-show[1],
@@ -77,14 +88,17 @@ format.coverLetter::
 	A boolean that controls whether to generate a cover-letter when
 	format-patch is invoked, but in addition can be set to "auto", to
 	generate a cover-letter only when there's more than one patch.
+	Default is false.
 
 format.outputDirectory::
 	Set a custom directory to store the resulting files instead of the
-	current working directory.
+	current working directory. All directory components will be created.
 
 format.useAutoBase::
 	A boolean value which lets you enable the `--base=auto` option of
-	format-patch by default.
+	format-patch by default. Can also be set to "whenAble" to allow
+	enabling `--base=auto` if a suitable base is available, but to skip
+	adding base info otherwise without the format dying.
 
 format.notes::
 	Provides the default value for the `--notes` option to
@@ -99,4 +113,20 @@ If one wishes to use the ref `ref/notes/true`, please use that literal
 instead.
 +
 This configuration can be specified multiple times in order to allow
-multiple notes refs to be included.
+multiple notes refs to be included. In that case, it will behave
+similarly to multiple `--[no-]notes[=]` options passed in. That is, a
+value of `true` will show the default notes, a value of `<ref>` will
+also show notes from that notes ref and a value of `false` will negate
+previous configurations and not show notes.
++
+For example,
++
+------------
+[format]
+	notes = true
+	notes = foo
+	notes = false
+	notes = bar
+------------
++
+will only show notes from `refs/notes/bar`.