Builtin-ify git-notes

The builtin-ification includes some minor behavioural changes to the
command-line interface: It is no longer allowed to mix the -m and -F
arguments, and it is not allowed to use multiple -F options.

As part of the builtin-ification, we add the commit_notes() function
to the builtin API. This function (together with the notes.h API) can
be easily used from other builtins to manipulate the notes tree.

Also includes needed changes to t3301.

This patch has been improved by the following contributions:
- Stephen Boyd: Use die() instead of fprintf(stderr, ...) followed by exit(1)

Cc: Stephen Boyd <bebarino@gmail.com>
Signed-off-by: Johan Herland <johan@herland.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git.c

@@ -343,6 +343,7 @@ static void handle_internal_command(int argc, const char **argv)
 		{ "mktree", cmd_mktree, RUN_SETUP },
 		{ "mv", cmd_mv, RUN_SETUP | NEED_WORK_TREE },
 		{ "name-rev", cmd_name_rev, RUN_SETUP },
+		{ "notes", cmd_notes, RUN_SETUP },
 		{ "pack-objects", cmd_pack_objects, RUN_SETUP },
 		{ "pack-redundant", cmd_pack_redundant, RUN_SETUP },
 		{ "patch-id", cmd_patch_id },