gpg: Make function mk_datestr public.
* g10/keydb.h (MK_DATESTR_SIZE): New. * g10/keyid.c (mk_datestr): Make public. Add arg bufsize and use snprintf. Change arg atime to u32. (datestr_from_pk): Simplify. (datestr_from_sig): Ditto. (expirestr_from_pk): Ditto. (expirestr_from_sig): Ditto. (revokestr_from_pk): Ditto.
Note that this also reduces the size of the static buffers from 16 to
11 which is sufficient for the string. In the past we added the 5
extra bytes to cope for bugs in gmtime which is now handles by
snprintf.
- Signed-off-by: Werner Koch <wk@gnupg.org>