Use gpgme_off_t and gpgme_ssize_t everywhere for GpgME++ 2.0
* src/mail.cpp (copy_data_property): Use gpgme_off_t instead of off_t. * src/mimedataprovider.cpp, src/mimedataprovider.h (MimeDataProvider::read, MimeDataProvider::write, MimeDataProvider::seek): Use gpgme_off_t and gpgme_ssize_t instead of off_t and ssize_t.
We need to use gpgme_off_t and gpgme_ssize_t instead of off_t and
ssize_t to avoid conflicting types for 64-bit builds.