RT17 updates

Remove prehistorical revision history,
Remove dead code,
Fix len vs. plen typo,
Check week/time valid flag in GSOF 16 message,
When getting week, make sure time reflects time of week from raw stream,
When possible also set time not just week when reading GSOF messages,
Allow .r17 file type in addition to .rt17,
The curve fit interval was incorrect when the fit flag was set.