From Ron Parker:

From Ron Parker:
1) upgrades the XML time parser to be more robust.  It now recognizes and
   correctly parses non-Zulu timestamps and timestamps with fractional
   seconds (which are truncated rather than rounded, but a motivated coder
   with time on his hands could change that.)
2) adds a field "exported" to struct geocache_data and fills it in with
   the appropriate value (the value from the groundspeak:exported tag on
   the waypoint if one exists, else the timestamp from the gpx/time element.)
3) adds (or replaces) the groundspeak:exported tag on output for any waypoint
   that contains a groundspeak:cache element.
4) adds the gpx/time element to any output GPX file, using the current time.
5) modifies the duplicate filter to prefer throwing away waypoints with older
   or unspecified "exported" dates over those with newer dates.