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-format-patch.txt

@@ -17,12 +17,14 @@ SYNOPSIS
 		   [--signature-file=<file>]
 		   [-n | --numbered | -N | --no-numbered]
 		   [--start-number <n>] [--numbered-files]
-		   [--in-reply-to=Message-Id] [--suffix=.<sfx>]
+		   [--in-reply-to=<message id>] [--suffix=.<sfx>]
 		   [--ignore-if-in-upstream]
-		   [--rfc] [--subject-prefix=Subject-Prefix]
+		   [--cover-from-description=<mode>]
+		   [--rfc] [--subject-prefix=<subject prefix>]
 		   [(--reroll-count|-v) <n>]
 		   [--to=<email>] [--cc=<email>]
 		   [--[no-]cover-letter] [--quiet]
+		   [--[no-]encode-email-headers]
 		   [--no-notes | --notes[=<ref>]]
 		   [--interdiff=<previous>]
 		   [--range-diff=<previous> [--creation-factor=<percent>]]
@@ -66,7 +68,8 @@ they are created in the current working directory. The default path
 can be set with the `format.outputDirectory` configuration option.
 The `-o` option takes precedence over `format.outputDirectory`.
 To store patches in the current working directory even when
-`format.outputDirectory` points elsewhere, use `-o .`.
+`format.outputDirectory` points elsewhere, use `-o .`. All directory
+components will be created.
 
 By default, the subject of a single patch is "[PATCH] " followed by
 the concatenation of lines from the commit message up to the first blank
@@ -159,9 +162,9 @@ Beware that the default for 'git send-email' is to thread emails
 itself.  If you want `git format-patch` to take care of threading, you
 will want to ensure that threading is disabled for `git send-email`.
 
---in-reply-to=Message-Id::
+--in-reply-to=<message id>::
 	Make the first mail (or all the mails with `--no-thread`) appear as a
-	reply to the given Message-Id, which avoids breaking threads to
+	reply to the given <message id>, which avoids breaking threads to
 	provide a new patch series.
 
 --ignore-if-in-upstream::
@@ -171,9 +174,29 @@ will want to ensure that threading is disabled for `git send-email`.
 	patches being generated, and any patch that matches is
 	ignored.
 
---subject-prefix=<Subject-Prefix>::
+--cover-from-description=<mode>::
+	Controls which parts of the cover letter will be automatically
+	populated using the branch's description.
++
+If `<mode>` is `message` or `default`, the cover letter subject will be
+populated with placeholder text. The body of the cover letter will be
+populated with the branch's description. This is the default mode when
+no configuration nor command line option is specified.
++
+If `<mode>` is `subject`, the first paragraph of the branch description will
+populate the cover letter subject. The remainder of the description will
+populate the body of the cover letter.
++
+If `<mode>` is `auto`, if the first paragraph of the branch description
+is greater than 100 bytes, then the mode will be `message`, otherwise
+`subject` will be used.
++
+If `<mode>` is `none`, both the cover letter subject and body will be
+populated with placeholder text.
+
+--subject-prefix=<subject prefix>::
 	Instead of the standard '[PATCH]' prefix in the subject
-	line, instead use '[<Subject-Prefix>]'. This
+	line, instead use '[<subject prefix>]'. This
 	allows for useful naming of a patch series, and can be
 	combined with the `--numbered` option.
 
@@ -231,6 +254,13 @@ feeding the result to `git send-email`.
 	containing the branch description, shortlog and the overall diffstat.  You can
 	fill in a description in the file before sending it out.
 
+--encode-email-headers::
+--no-encode-email-headers::
+	Encode email headers that have non-ASCII characters with
+	"Q-encoding" (described in RFC 2047), instead of outputting the
+	headers verbatim. Defaults to the value of the
+	`format.encodeEmailHeaders` configuration variable.
+
 --interdiff=<previous>::
 	As a reviewer aid, insert an interdiff into the cover letter,
 	or as commentary of the lone patch of a 1-patch series, showing
@@ -311,10 +341,12 @@ you can use `--suffix=-patch` to get `0001-description-of-my-change-patch`.
   Output an all-zero hash in each patch's From header instead
   of the hash of the commit.
 
---base=<commit>::
+--[no-]base[=<commit>]::
 	Record the base tree information to identify the state the
 	patch series applies to.  See the BASE TREE INFORMATION section
-	below for details.
+	below for details. If <commit> is "auto", a base commit is
+	automatically chosen. The `--no-base` option overrides a
+	`format.useAutoBase` configuration.
 
 --root::
 	Treat the revision argument as a <revision range>, even if it
@@ -330,8 +362,9 @@ CONFIGURATION
 -------------
 You can specify extra mail header lines to be added to each message,
 defaults for the subject prefix and file suffix, number patches when
-outputting more than one patch, add "To" or "Cc:" headers, configure
-attachments, and sign off patches with configuration variables.
+outputting more than one patch, add "To:" or "Cc:" headers, configure
+attachments, change the patch output directory, and sign off patches
+with configuration variables.
 
 ------------
 [format]
@@ -343,7 +376,9 @@ attachments, and sign off patches with configuration variables.
 	cc = <email>
 	attach [ = mime-boundary-string ]
 	signOff = true
-	coverletter = auto
+	outputDirectory = <directory>
+	coverLetter = auto
+	coverFromDescription = auto
 ------------