20131216 fix update of pester queue

This updates the reminder/pester for unavailable users to check and make use of the user's 'Become Available' date if it exists. It also fixes the code so that the 'last pester' time stamp is updated correctly, and improves the test function so that the items added to the queue are processed immediately (without any further additions to the queue) without requiring cron to run. This pull request is related to the closed issue #209 and closed #Issue #361/Pull #361.