Add patches for gpgsm offline mode
* Makefile.am (EXTRA_DIST): Add patches. * patches/gnupg2-2.0.28/0006-gpgsm-Add-command-option-offline.patch, patches/gpgme-1.5.5/ 0001-Add-offline-mode-support-for-CMS-keylisting.patch: New.
The patch to gnupg is a backport from GnuPG 2.1.