* verify.c (_gpgme_release_verify_result): Rename RES to RESULT.
Rename R2 to NEXT_RESULT.
(intersect_stati): Rename RES to RESULT.
(gpgme_get_sig_status): Likewise. Do not check return_type, but
the member verify of result.
(gpgme_get_sig_key): Likewise.
* sign.c (_gpgme_release_sign_result): Rename RES to RESULT. If
RESULT is zero, return.
(sign_status_handler, command_handler): Do not check return_type,
but the member sign of result.
(gpgme_op_sign): Likewise. Drop assertion.
* encrypt.c (_gpgme_release_encrypt_result): Rename RES to RESULT.
If RESULT is zero, return.
(encrypt_status_handler): Do not check return_type, but the member
encrypt of result.
(gpgme_op_encrypt): Likewise. Drop assertion.
* decrypt.c (_gpgme_release_decrypt_result): Rename RES to RESULT.
(create_result_struct): Do not set result_type.
(command_handler, decrypt_status_handler): Do not check
return_type, but the member decrypt of result.
(gpgme_op_decrypt): Likewise. Drop assertion.
* context.h (enum ResultType): Removed.
(struct gpgme_context_s): Remove member result_type.
(struct result): Replaces union result.
* gpgme.c: Include string.h.
(_gpgme_release_result): Release all members of c->result, which
is now a struct. Zero out all members of the struct afterwards.
