* common/call-gpg.c (struct writer_thread_parms): Add field 'stream'.
(writer_thread_main): Support reading from a stream.
(start_writer): Add stream argument.
(struct reader_thread_parms): Add field 'stream'.
(reader_thread_main): Support writing to a stream.
(start_reader): Add stream argument.
(_gpg_encrypt): Add stream api.
(gpg_encrypt_blob): Adapt accordingly.
(gpg_encrypt_stream): New function.
(_gpg_decrypt): Add stream api.
(gpg_decrypt_blob): Adapt accordingly.
(gpg_decrypt_stream): New function.
* common/call-gpg.h (gpg_encrypt_stream): New prototype.
(gpg_decrypt_stream): Likewise.