estream: Track the kind of backend used.
* src/estream.c (struct _gpgrt_stream_internal): Add 'kind'. (init_stream_obj): New parameter 'kind', initialize field. (es_create): New parameter 'kind'. Update all callers. * src/gpgrt-int.h (gpgrt_stream_backend_kind_t): New type.
- Signed-off-by: Justus Winter <justus@g10code.com>