Switched filter_archive time stamping to the GPS time (bug #458).

This required working "tconvert" call to get the GPS time during "make install" phase.
Also requires new symmetricom driver loaded on the front-end to enable /proc/gps support.
The code is backwards compatible: if either tconvert or /proc/gps is not found, the old
time stamp based on the UNIX system time is used.


git-svn-id: https://redoubt.ligo-wa.caltech.edu/svn/advLigoRTS/trunk@3391 6dcd42c9-f523-4c6d-aada-af552506706e