gpg: Allow searching for user ids in a keybox.
* kbx/keybox-search.c (blob_cmp_name): Add arg X509 and adjust for PGP use. Change callers. (blob_cmp_mail): Add arg X509 and find the mailbox offset for PGP. Chnage callers. (has_subject_or_alt): Rename to has_username. (has_username): Allow blobtype PGP. (has_mail): Ditto.