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>

merge-base.c

@@ -236,6 +236,8 @@ int main(int argc, char **argv)
 	struct commit *rev1, *rev2;
 	unsigned char rev1key[20], rev2key[20];
 
+	setup_git_directory();
+
 	while (1 < argc && argv[1][0] == '-') {
 		char *arg = argv[1];
 		if (!strcmp(arg, "-a") || !strcmp(arg, "--all"))