gpgsm: Strip trailing zeroes from detached signatures.
* common/ksba-io-support.c: Include tlv.h (struct reader_cb_parm_s): Add new fields. (starts_with_sequence): New. (simple_reader_cb): Handle stripping. * common/ksba-io-support.h (GNUPG_KSBA_IO_STRIP): New. (gnupg_ksba_create_reader): Handle the new flag. * sm/verify.c (gpgsm_verify): Use the new flag for detached signatures.
Note that this works only if --assume-binary is given. The use case
for the feature is PDF signature checking where the PDF specs require
that the detached signature is padded with zeroes.
(cherry picked from commit 2a13f7f9dc75265ece649e30fecd3dc694b1240e)