Move 'builtin-*' into a 'builtin/' subdirectory

This shrinks the top-level directory a bit, and makes it much more
pleasant to use auto-completion on the thing. Instead of

	[torvalds@nehalem git]$ em buil<tab>
	Display all 180 possibilities? (y or n)
	[torvalds@nehalem git]$ em builtin-sh
	builtin-shortlog.c     builtin-show-branch.c  builtin-show-ref.c
	builtin-shortlog.o     builtin-show-branch.o  builtin-show-ref.o
	[torvalds@nehalem git]$ em builtin-shor<tab>
	builtin-shortlog.c  builtin-shortlog.o
	[torvalds@nehalem git]$ em builtin-shortlog.c

you get

	[torvalds@nehalem git]$ em buil<tab>		[type]
	builtin/   builtin.h
	[torvalds@nehalem git]$ em builtin		[auto-completes to]
	[torvalds@nehalem git]$ em builtin/sh<tab>	[type]
	shortlog.c     shortlog.o     show-branch.c  show-branch.o  show-ref.c     show-ref.o
	[torvalds@nehalem git]$ em builtin/sho		[auto-completes to]
	[torvalds@nehalem git]$ em builtin/shor<tab>	[type]
	shortlog.c  shortlog.o
	[torvalds@nehalem git]$ em builtin/shortlog.c

which doesn't seem all that different, but not having that annoying
break in "Display all 180 possibilities?" is quite a relief.

NOTE! If you do this in a clean tree (no object files etc), or using an
editor that has auto-completion rules that ignores '*.o' files, you
won't see that annoying 'Display all 180 possibilities?' message - it
will just show the choices instead.  I think bash has some cut-off
around 100 choices or something.

So the reason I see this is that I'm using an odd editory, and thus
don't have the rules to cut down on auto-completion.  But you can
simulate that by using 'ls' instead, or something similar.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/update-ref.c

@@ -0,0 +1,58 @@
+#include "cache.h"
+#include "refs.h"
+#include "builtin.h"
+#include "parse-options.h"
+
+static const char * const git_update_ref_usage[] = {
+	"git update-ref [options] -d <refname> [<oldval>]",
+	"git update-ref [options]    <refname> <newval> [<oldval>]",
+	NULL
+};
+
+int cmd_update_ref(int argc, const char **argv, const char *prefix)
+{
+	const char *refname, *oldval, *msg=NULL;
+	unsigned char sha1[20], oldsha1[20];
+	int delete = 0, no_deref = 0, flags = 0;
+	struct option options[] = {
+		OPT_STRING( 'm', NULL, &msg, "reason", "reason of the update"),
+		OPT_BOOLEAN('d', NULL, &delete, "deletes the reference"),
+		OPT_BOOLEAN( 0 , "no-deref", &no_deref,
+					"update <refname> not the one it points to"),
+		OPT_END(),
+	};
+
+	git_config(git_default_config, NULL);
+	argc = parse_options(argc, argv, prefix, options, git_update_ref_usage,
+			     0);
+	if (msg && !*msg)
+		die("Refusing to perform update with empty message.");
+
+	if (delete) {
+		if (argc < 1 || argc > 2)
+			usage_with_options(git_update_ref_usage, options);
+		refname = argv[0];
+		oldval = argv[1];
+	} else {
+		const char *value;
+		if (argc < 2 || argc > 3)
+			usage_with_options(git_update_ref_usage, options);
+		refname = argv[0];
+		value = argv[1];
+		oldval = argv[2];
+		if (get_sha1(value, sha1))
+			die("%s: not a valid SHA1", value);
+	}
+
+	hashclr(oldsha1); /* all-zero hash in case oldval is the empty string */
+	if (oldval && *oldval && get_sha1(oldval, oldsha1))
+		die("%s: not a valid old SHA1", oldval);
+
+	if (no_deref)
+		flags = REF_NODEREF;
+	if (delete)
+		return delete_ref(refname, oldval ? oldsha1 : NULL, flags);
+	else
+		return update_ref(msg, refname, sha1, oldval ? oldsha1 : NULL,
+				  flags, DIE_ON_ERR);
+}