Api should validate & transform timestamp fields as a date (accept strtotime)

Sigh - no point - PEAR in it's wisdom decided no-one would ever want to save to a timestamp field .... here is the comment

// dont insert data into mysql timestamps
// use query() if you really want to do this!!!!

Well - hopefully symphony will be more sympathetic - in the mean time I can fool pear by making it a timestamp field without telling it (since in this particular instance it is in an extension & since we've been running 'dont-tell-PEAR' fields like this on core tables like civicrm_mailing_scheduled_date for the last 2 years

Here's the commit

https://github.com/eileenmcnaughton/civicrm-core/commit/a88272ffdec76f2b4ee1fd239e315b47ad2feb0d