Synch with Gnus trunk.

2010-06-10  Dan Christensen  <jdc@uwo.ca>
 * gnus-util.el (gnus-user-date): Use gnus-date-get-time.
 (gnus-dd-mmm): Use gnus-date-get-time.
 * gnus-sum.el (gnus-thread-latest-date): Use gnus-date-get-time and
 simplify logic.
 (gnus-summary-limit-to-age): Use gnus-date-get-time.
 (gnus-sort-threads): emit message if gnus-sort-threads-loop used.