corrupt session groups can have packet files with multiple APIDs
we handel this by filtering these out and skipping to the next stamp

Because merge was only considering stamp/apid packets for the same
stamp/apid with different byte size were being treated as equal. It now
always treats packets/group with more bytes as more gooder.

This version has a major fix regarding merging of VIIRS data. Do not use
any previous version for VIIRS merges.