* src/gpgme.h.in (_gpgme_op_decrypt_result): Add field session_hash.
(gpgme_decrypt_flags_t): Add flag GPGME_DECRYPT_SESSION_HASH.
(gpgme_status_code_t): Add flags GPGME_STATUS_SESSION_HASH.
* src/status-table.c (status_table): Add "SESSION_HASH".
* src/decrypt.c (release_op_data): Free new field.
(_gpgme_decrypt_status_handler): Handle new status code.
* src/engine-gpg.c (gpg_decrypt): Implement
  GPGME_DECRYPT_SESSION_HASH.
* tests/run-decrypt.c (print_result): Print session_hash.
(main): Add option --show-session-hash.