Don't use glue.gpstime for GPS conversions

Currently scripts like ligolw_segments_from_cats_dqsegdb are using glue.gpstime for GPS conversions:

https://github.com/ligovirgo/dqsegdb/blob/87f492ad74d2853ba3f9ef0784cefbbb88fd482a/bin/ligolw_segments_from_cats_dqsegdb#L271

This module has manual handling of leap-seconds, and hasn't been updated for any of the last 4 leap seconds (at least), so all conversions are now 4-seconds out:

>>> import time
>>> from glue.gpstime import GpsSecondsFromPyUTC
>>> from gwpy.time import tconvert
>>> print(GpsSecondsFromPyUTC(time.time()), tconvert('now'))
1326471223 1326471227

All instances of GpsSecondsFromPyUTC should be replaced with something that automatically updates its leap-seconds knowledge, probably astropy.time, gwpy.time, or the standalone gpstime module (from the LIGO CDS group).