Provide file sizes to Gen2 when archiving PFS frames

Currently, when PFS asks Gen2 to archive a frame, it constructs a frame list containing tuples of the form (frameid, path).  Gen2 will accept this form, but has no way to do any kind of quick check to ensure that the file was copied in complete form.

PFS should add the file size as a third component of every tuple in the frame list: (frameid, path, size_in_bytes). Then the Gen2 archiver can at least perform a perfunctory size comparison as a quick check.