git-sh-setup.sh: use dashdash with basename call

Calling basename on a argument that starts with a dash, like a login
shell, will result in an error. Add '--' before the argument so that
the argument is interpreted properly.

Signed-off-by: Dan Wyand <danwyand@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-sh-setup.sh

@@ -81,7 +81,7 @@ if test -n "$OPTIONS_SPEC"; then
 		echo exit $?
 	)"
 else
-	dashless=$(basename "$0" | sed -e 's/-/ /')
+	dashless=$(basename -- "$0" | sed -e 's/-/ /')
 	usage() {
 		die "usage: $dashless $USAGE"
 	}