git-am: Make it easier to see which patch failed

When git-am fails it's not always easy to see which patch failed,
since it's often hidden by a lot of error messages.
Add an extra line which prints the name of the failed patch just
before the resolve message to make it easier to find.

Signed-off-by: Jonas Flodén <jonas@floden.nu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-am.sh

@@ -501,7 +501,7 @@ do
 	fi
 	if test $apply_status != 0
 	then
-		echo Patch failed at $msgnum.
+		echo "Patch failed at $msgnum $FIRSTLINE"
 		stop_here_user_resolve $this
 	fi