"git tag -u keyname" broken

"git tag -u keyname" broken

Commit 396865859918e9c7bf8ce74aae137c57da134610 broke signed tags using
the "-u" flag when it made builtin-tag.c use parse_options() to parse its
arguments (but it quite possibly was broken even before that, by the
builtin rewrite).

It used to be that passing the signing ID with the -u parameter also
(obviously!) implied that you wanted to sign and annotate the tag, but
that logic got dropped. It also totally ignored the actual key ID that was
passed in.

This reinstates it all.

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