* g10/options.h (COMPAT_PARALLELIZED): New.
* g10/filter.h (md_thd_filter_context_t): New type.
(md_thd_filter_set_md, md_thd_filter): New.
* g10/gpg.c (compatibility_flags): Update to support
COMPAT_PARALLELIZED.
* g10/mdfilter.c (struct md_thd_filter_context): New.
(lock_md, unlock_md, get_buffer_to_hash, put_buffer_to_recv): New.
(get_buffer_to_fill, put_buffer_to_send, md_thread): New.
(md_thd_filter, md_thd_filter_set_md): New.
* g10/sign.c (sign_file): Add support for md_thd_filter.
(sign_symencrypt_file): Likewise.