gpg: Use AKL for angle bracketed mail address with -r.

* g10/getkey.c (get_pubkey_byname): Extend is_mbox checking.
(get_best_pubkey_byname): Ditto.

With this patch it is now possible to use

gpg -e -r '<foo@example.org>'

and auto key locate will find the key. Without that a plain mail
address; i.e.

gpg -e -r 'foo@example.org'

was required.

• GnuPG-bug-id: T4726
• Signed-off-by: Werner Koch <wk@gnupg.org>