* src/gpgrt-int.h (struct _gpgrt_stream_internal): Add field "wipe".
* src/estream.c (mem_free2): New.
(struct estream_cookie_mem): Add flag "wipe".
(func_mem_create): Add arg wipe.
(func_mem_destroy): Wipe.
(X_WIPE): New.
(parse_mode): Parse "wipe" mode flag.
(init_stream_obj): Set it.
(do_close): Wipe internal struct with its static buffers.
(doreadline): Pass wipe mode along to help buffer.
(_gpgrt_mopen): Pass wipe mode.
(_gpgrt_fopenmem): Ditto.