Usage message clean-up, take #2

There were some problems with the usage message clean-up patch
series. I hadn't realised that subdirectory aware scripts can't source
git-sh-setup. I propose that we change this and let the scripts which
are subdirectory aware set a variable, SUBDIRECTORY_OK, before they
source git-sh-setup.

The scripts will also set USAGE and possibly LONG_USAGE before they
source git-sh-setup. If LONG_USAGE isn't set it defaults to USAGE.

If we go this way it's easy to catch --help in git-sh-setup, print the
(long) usage message to stdout and exit cleanly. git-sh-setup can
define a 'usage' shell function which can be called by the scripts to
print the short usage string to stderr and exit non-cleanly. It will
also be easy to change $0 to basename $0 or something else, if would
like to do that sometime in the future.

What follows is a patch to convert a couple of the commands to this
style. If it's ok with everyone to do it this way I will convert the
rest of the scripts too.

[jc: thrown in to proposed updates queue for comments.]

Signed-off-by: Junio C Hamano <junkio@cox.net>

git-sh-setup.sh

@@ -11,13 +11,37 @@
 # exporting it.
 unset CDPATH
 
-: ${GIT_DIR=.git}
-: ${GIT_OBJECT_DIRECTORY="$GIT_DIR/objects"}
-
 die() {
 	echo >&2 "$@"
 	exit 1
 }
 
-# Make sure we are in a valid repository of a vintage we understand.
-GIT_DIR="$GIT_DIR" git-var GIT_AUTHOR_IDENT >/dev/null || exit
+usage() {
+	die "Usage: $0 $USAGE"
+}
+
+if [ -z "$LONG_USAGE" ]
+then
+	LONG_USAGE="Usage: $0 $USAGE"
+else
+	LONG_USAGE="Usage: $0 $USAGE
+
+$LONG_USAGE"
+fi
+
+case "$1" in
+	--h|--he|--hel|--help)
+	echo "$LONG_USAGE"
+	exit
+esac
+
+if [ -z "$SUBDIRECTORY_OK" ]
+then
+	: ${GIT_DIR=.git}
+	: ${GIT_OBJECT_DIRECTORY="$GIT_DIR/objects"}
+
+	# Make sure we are in a valid repository of a vintage we understand.
+	GIT_DIR="$GIT_DIR" git-var GIT_AUTHOR_IDENT >/dev/null || exit
+else
+	GIT_DIR=$(git-rev-parse --git-dir) || exit
+fi