Format GPG errors (bug#9255).

Format GPG errors (bug#9255).

* epg.el (epg--status-KEYEXPIRED, epg--status-KEYREVOKED): Fix typo.
(epg-error-to-string, epg-errors-to-string): New function.
(epg-wait-for-completion): Reverse errors list.
(epg--check-error-for-decrypt, epg-sign-file, epg-sign-string)
(epg-encrypt-file, epg-encrypt-string, epg-export-keys-to-file)
(epg--import-keys-1, epg-receive-keys, epg-delete-keys)
(epg-sign-keys, epg-generate-key-from-file)
(epg-generate-key-from-string): Format errors by using
epg-errors-to-string (bug#9255).
(epg--status-INV_SGNR, epg--status-NO_SGNR): New status handler.