json: Add command "getmore" to gpgme-json.
* src/gpgme-json.c (MIN_REPLY_CHUNK_SIZE): New const. (DEF_REPLY_CHUNK_SIZE): New const. (MAX_REPLY_CHUNK_SIZE): New const. (pending_data): New var. (add_base64_to_object): Chnage to take a plain data pointer. (get_chunksize): New. (make_data_object): New. (op_encrypt): Get chunksize and use make_data_object. (op_getmore): New. (process_request): Release pending data for all commands but "getmore" and "help".
Native messaging has a limit on the data it may receive in one
request. Thus the caller needs to watch for the "more" flag and
request the remaining data using "getmore" in a loop.
- Signed-off-by: Werner Koch <wk@gnupg.org>