Use 64bit type internally for package archive size & offset

Use 64bit type internally for package archive size & offset
- cpio "new" ascii format limits individual files to UINT32_MAX, no such
  limit on the entire archive though
- RPMSIGTAG_PAYLOADSIZE is 32bit type atm, assert that the archive size
  fits to UINT32_MAX despite internal presentation being larger
- FD_t limits the real archive to rpm_off_t still