* src/estream.c (X_SAMETHREAD, X_SYSOPEN): New macros.
(parse_mode): Rework how information flows from here to 'es_create'.
Instead of using an integer flag per mode, use flags.
(init_stream_obj): Adapt accordingly.
(es_create): Likewise.
(_gpgrt_fopen): Likewise.
(_gpgrt_mopen): Likewise.
(_gpgrt_fopenmem): Likewise.
(_gpgrt_fopencookie): Likewise.
(_gpgrt_fdopen): Likewise.
(_gpgrt_fpopen): Likewise.
(do_w32open): Likewise.
(_gpgrt_freopen): Likewise.