allow git-bundle to create bottomless bundle

While "git bundle" was a useful way to sneakernet incremental
changes, we did not allow:

	$ git bundle create v2.6.20.bndl v2.6.20

to create a bundle that contains the whole history to a
well-known good revision.  Such a bundle can be mirrored
everywhere, and people can prime their repository with it to
reduce the load on the repository that serves near the tip of
the development.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-bundle.c

@@ -208,6 +208,10 @@ static int create_bundle(struct bundle_header *header, const char *path,
 	struct rev_info revs;
 	struct child_process rls;
 
+	/*
+	 * NEEDSWORK: this should use something like lock-file
+	 * to create temporary that is cleaned up upon error.
+	 */
 	bundle_fd = (!strcmp(path, "-") ? 1 :
 			open(path, O_CREAT | O_EXCL | O_WRONLY, 0666));
 	if (bundle_fd < 0)
@@ -267,8 +271,12 @@ static int create_bundle(struct bundle_header *header, const char *path,
 		 * Make sure the refs we wrote out is correct; --max-count and
 		 * other limiting options could have prevented all the tips
 		 * from getting output.
+		 *
+		 * Non commit objects such as tags and blobs do not have
+		 * this issue as they are not affected by those extra
+		 * constraints.
 		 */
-		if (!(e->item->flags & SHOWN)) {
+		if (!(e->item->flags & SHOWN) && e->item->type == OBJ_COMMIT) {
 			warning("ref '%s' is excluded by the rev-list options",
 				e->name);
 			continue;

t/t5510-fetch.sh

@@ -145,4 +145,12 @@ test_expect_success 'bundle does not prerequisite objects' '
 	test 4 = $(git verify-pack -v bundle.pack | wc -l)
 '
 
+test_expect_success 'bundle should be able to create a full history' '
+
+	cd "$D" &&
+	git tag -a -m '1.0' v1.0 master &&
+	git bundle create bundle4 v1.0
+
+'
+
 test_done