Disallow working directory commands in a bare repository.

If the user tries to run a porcelainish command which requires
a working directory in a bare repository they may get unexpected
results which are difficult to predict and may differ from command
to command.

Instead we should detect that the current repository is a bare
repository and refuse to run the command there, as there is no
working directory associated with it.

[jc: updated Shawn's original somewhat -- bugs are mine.]

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

git-sh-setup.sh

@@ -36,6 +36,11 @@ is_bare_repository () {
 	esac
 }
 
+require_work_tree () {
+	test $(is_bare_repository) = false ||
+	die "fatal: $0 cannot be used without a working tree."
+}
+
 if [ -z "$LONG_USAGE" ]
 then
 	LONG_USAGE="Usage: $0 $USAGE"