Make rpmfiFSize() return rpm_loff_t type, fixup callers

Make rpmfiFSize() return rpm_loff_t type, fixup callers
- Internally file sizes are still stored as 32bit, going to 64bit wouldn't
  make much sense (would only waste memory for nothing) as long as we're
  bound by cpio's 32bit per-file limit. Being "64bit ready" for filesizes
  doesn't hurt anything though...