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/merge-base.c

@@ -0,0 +1,63 @@
+#include "builtin.h"
+#include "cache.h"
+#include "commit.h"
+#include "parse-options.h"
+
+static int show_merge_base(struct commit **rev, int rev_nr, int show_all)
+{
+	struct commit_list *result;
+
+	result = get_merge_bases_many(rev[0], rev_nr - 1, rev + 1, 0);
+
+	if (!result)
+		return 1;
+
+	while (result) {
+		printf("%s\n", sha1_to_hex(result->item->object.sha1));
+		if (!show_all)
+			return 0;
+		result = result->next;
+	}
+
+	return 0;
+}
+
+static const char * const merge_base_usage[] = {
+	"git merge-base [-a|--all] <commit> <commit>...",
+	NULL
+};
+
+static struct commit *get_commit_reference(const char *arg)
+{
+	unsigned char revkey[20];
+	struct commit *r;
+
+	if (get_sha1(arg, revkey))
+		die("Not a valid object name %s", arg);
+	r = lookup_commit_reference(revkey);
+	if (!r)
+		die("Not a valid commit name %s", arg);
+
+	return r;
+}
+
+int cmd_merge_base(int argc, const char **argv, const char *prefix)
+{
+	struct commit **rev;
+	int rev_nr = 0;
+	int show_all = 0;
+
+	struct option options[] = {
+		OPT_BOOLEAN('a', "all", &show_all, "outputs all common ancestors"),
+		OPT_END()
+	};
+
+	git_config(git_default_config, NULL);
+	argc = parse_options(argc, argv, prefix, options, merge_base_usage, 0);
+	if (argc < 2)
+		usage_with_options(merge_base_usage, options);
+	rev = xmalloc(argc * sizeof(*rev));
+	while (argc-- > 0)
+		rev[rev_nr++] = get_commit_reference(*argv++);
+	return show_merge_base(rev, rev_nr, show_all);
+}