am: add the --gpg-sign option

Signed-off-by: Nicolas Vigier <boklm@mars-attacks.org>
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-am.txt

@@ -14,7 +14,7 @@ SYNOPSIS
 	 [--ignore-date] [--ignore-space-change | --ignore-whitespace]
 	 [--whitespace=<option>] [-C<n>] [-p<n>] [--directory=<dir>]
 	 [--exclude=<path>] [--include=<path>] [--reject] [-q | --quiet]
-	 [--[no-]scissors]
+	 [--[no-]scissors] [-S[<keyid>]]
 	 [(<mbox> | <Maildir>)...]
 'git am' (--continue | --skip | --abort)
 
@@ -119,6 +119,10 @@ default.   You can use `--no-utf8` to override this.
 	Skip the current patch.  This is only meaningful when
 	restarting an aborted patch.
 
+-S[<keyid>]::
+--gpg-sign[=<keyid>]::
+	GPG-sign commits.
+
 --continue::
 -r::
 --resolved::

git-am.sh

@@ -38,6 +38,7 @@ abort           restore the original branch and abort the patching operation.
 committer-date-is-author-date    lie about committer date
 ignore-date     use current timestamp for author date
 rerere-autoupdate update the index with reused conflict resolution if possible
+S,gpg-sign?     GPG-sign commits
 rebasing*       (internal use for git-rebase)"
 
 . git-sh-setup
@@ -375,6 +376,7 @@ git_apply_opt=
 committer_date_is_author_date=
 ignore_date=
 allow_rerere_autoupdate=
+gpg_sign_opt=
 
 if test "$(git config --bool --get am.keepcr)" = true
 then
@@ -436,6 +438,10 @@ it will be removed. Please do not use it anymore."
 		keepcr=t ;;
 	--no-keep-cr)
 		keepcr=f ;;
+	--gpg-sign)
+		gpg_sign_opt=-S ;;
+	--gpg-sign=*)
+		gpg_sign_opt="-S${1#--gpg-sign=}" ;;
 	--)
 		shift; break ;;
 	*)
@@ -900,7 +906,8 @@ did you forget to use 'git add'?"
 			GIT_COMMITTER_DATE="$GIT_AUTHOR_DATE"
 			export GIT_COMMITTER_DATE
 		fi &&
-		git commit-tree $tree ${parent:+-p} $parent <"$dotest/final-commit"
+		git commit-tree ${parent:+-p} $parent ${gpg_sign_opt:+"$gpg_sign_opt"} $tree  \
+			<"$dotest/final-commit"
 	) &&
 	git update-ref -m "$GIT_REFLOG_ACTION: $FIRSTLINE" HEAD $commit $parent ||
 	stop_here $this