Teach git-local-fetch the --stdin switch

This makes it possible to fetch many commits (refs) at once, greatly
speeding up cg-clone.

Signed-off-by: Petr Baudis <pasky@suse.cz>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/git-local-fetch.txt

@@ -29,6 +29,12 @@ OPTIONS
         Writes the commit-id into the filename under $GIT_DIR/refs/<filename> on
         the local end after the transfer is complete.
 
+--stdin::
+	Instead of a commit id on the commandline (which is not expected in this
+	case), 'git-local-fetch' expects lines on stdin in the format
+
+		<commit-id>['\t'<filename-as-in--w>]
+
 Author
 ------
 Written by Junio C Hamano <junkio@cox.net>