core: Make listing of signatures work if only secret keys are listed
* src/engine-gpg.c (gpg_keylist_build_options): Add "--with-sig-check" argument if signatures shall be listed. * tests/gpg/t-keylist-secret-sig.c: New. * tests/gpg/Makefile.am (c_tests): Add new test.
- GnuPG-bug-id: T3580