Big tool rename.

As promised, this is the "big tool rename" patch.  The primary differences
since 0.99.6 are:

  (1) git-*-script are no more.  The commands installed do not
      have any such suffix so users do not have to remember if
      something is implemented as a shell script or not.

  (2) Many command names with 'cache' in them are renamed with
      'index' if that is what they mean.

There are backward compatibility symblic links so that you and
Porcelains can keep using the old names, but the backward
compatibility support  is expected to be removed in the near
future.

Signed-off-by: Junio C Hamano <junkio@cox.net>
diff --git a/entry.c b/entry.c
index 15b8fda..b8426db 100644
--- a/entry.c
+++ b/entry.c
@@ -76,7 +76,7 @@
 	if (!new || strcmp(type, "blob")) {
 		if (new)
 			free(new);
-		return error("git-checkout-cache: unable to read sha1 file of %s (%s)",
+		return error("git-checkout-index: unable to read sha1 file of %s (%s)",
 			path, sha1_to_hex(ce->sha1));
 	}
 	switch (ntohl(ce->ce_mode) & S_IFMT) {
@@ -84,28 +84,28 @@
 		fd = create_file(path, ntohl(ce->ce_mode));
 		if (fd < 0) {
 			free(new);
-			return error("git-checkout-cache: unable to create file %s (%s)",
+			return error("git-checkout-index: unable to create file %s (%s)",
 				path, strerror(errno));
 		}
 		wrote = write(fd, new, size);
 		close(fd);
 		free(new);
 		if (wrote != size)
-			return error("git-checkout-cache: unable to write file %s", path);
+			return error("git-checkout-index: unable to write file %s", path);
 		break;
 	case S_IFLNK:
 		memcpy(target, new, size);
 		target[size] = '\0';
 		if (symlink(target, path)) {
 			free(new);
-			return error("git-checkout-cache: unable to create symlink %s (%s)",
+			return error("git-checkout-index: unable to create symlink %s (%s)",
 				path, strerror(errno));
 		}
 		free(new);
 		break;
 	default:
 		free(new);
-		return error("git-checkout-cache: unknown file mode for %s", path);
+		return error("git-checkout-index: unknown file mode for %s", path);
 	}
 
 	if (state->refresh_cache) {
@@ -131,7 +131,7 @@
 			return 0;
 		if (!state->force) {
 			if (!state->quiet)
-				fprintf(stderr, "git-checkout-cache: %s already exists\n", path);
+				fprintf(stderr, "git-checkout-index: %s already exists\n", path);
 			return 0;
 		}