new-workdir: handle rev-parse --git-dir not always giving full path

rev-parse --git-dir outputs a full path - except for the single case
of when the path would be $(pwd)/.git, in which case it outputs simply
.git.  Check for this special case and handle it.

Signed-off-by: Julian Phillips <julian@quantumfyre.co.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/workdir/git-new-workdir

@@ -24,6 +24,11 @@ git_dir=$(cd "$orig_git" 2>/dev/null &&
   git rev-parse --git-dir 2>/dev/null) ||
   die "\"$orig_git\" is not a git repository!"
 
+if test "$git_dir" == ".git"
+then
+	git_dir="$orig_git/.git"
+fi
+
 # don't link to a workdir
 if test -L "$git_dir/config"
 then