* pgg-gpg.el (lookup-key-string): Use `call-process' instead of

* pgg-gpg.el (lookup-key-string): Use `call-process' instead of
`pgg-gpg-process-region'.
(encrypt-region): Use `pgg-process-when-success'; if the output
buffer is empty, don't copy errors, just return nil.
(decrypt-region): Likewise.
(verify-region): Check the contents of status buffer to looking
for `GOODSIG' response.
(sign-region): Accept optional argument `clearsign'.