git-applypatch: Usage string clean-up, emit usage string at incorrect invocation

Signed-off-by: Fredrik Kuivinen <freku045@student.liu.se>
Signed-off-by: Junio C Hamano <junkio@cox.net>

git-applypatch.sh

@@ -10,8 +10,12 @@
 ##	$3 - "info" file with Author, email and subject
 ##	$4 - optional file containing signoff to add
 ##
+
+USAGE='<msg> <patch> <info> [<signoff>]'
 . git-sh-setup
 
+[[ "$#" = "3" || "$#" = "4" ]] || usage
+
 final=.dotest/final-commit
 ##
 ## If this file exists, we ask before applying