Make the rest of commands work from a subdirectory.

These commands are converted to run from a subdirectory.

    commit-tree convert-objects merge-base merge-index mktag
    pack-objects pack-redundant prune-packed read-tree tar-tree
    unpack-file unpack-objects update-server-info write-tree

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

mktag.c

@@ -111,6 +111,8 @@ int main(int argc, char **argv)
 	if (argc != 1)
 		usage("cat <signaturefile> | git-mktag");
 
+	setup_git_directory();
+
 	// Read the signature
 	size = 0;
 	for (;;) {