Time.zone.now vs. Time.now

Time.now uses the local time, whereas Time.zone.now uses the Time
configured for use with the DB.  The comparisons/setters for the expires field should use Time.zone.now instead of Time.now, otherwise users in time zones other than the TZ zone will have problems with the comparisons.

@Roendal, apologies for the repeated pull requests related to this issue.  The last one was simply poor coding/testing on my part, but this one was at least due to a lack of familiarity with the rails time setups.

Thanks,
-Mike