allow git-am to run in a subdirectory

We just move to the top of the tree and proceed. This
shouldn't break any existing callers, since the behavior was
previously disallowed.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-am.sh

@@ -2,6 +2,7 @@
 #
 # Copyright (c) 2005, 2006 Junio C Hamano
 
+SUBDIRECTORY_OK=Yes
 OPTIONS_KEEPDASHDASH=
 OPTIONS_SPEC="\
 git-am [options] <mbox>|<Maildir>...
@@ -25,6 +26,7 @@ skip            skip the current patch"
 . git-sh-setup
 set_reflog_action am
 require_work_tree
+cd_to_toplevel
 
 git var GIT_COMMITTER_IDENT >/dev/null || exit