Copy account creation date from master to slave

When creating a new account on slave, set $user->created to same value as on Master.

We need this for Drupalcon Chicago (and possibly future Drupalcons). We want to honor Drupal accounts that were registered in 2001 with several perks like a mention in the booklet and a special badge on the web site.

In general, it makes sense for 'member since' data to be consistent across a family of sites. Optional, of course.