core: Add gpgme_data_set_flag to add more meta data to data objects.
* src/gpgme.h.in (gpgme_data_set_flag): New public function. * src/data.c (gpgme_data_set_flag): New. (_gpgme_data_get_size_hint): New. * src/data.h (strucy gpgme_data): Add field 'size_hint'. * src/gpgme.def, src/libgpgme.vers: Add new function. * src/conversion.c (_gpgme_string_to_off): New.
- Signed-off-by: Werner Koch <wk@gnupg.org>