CRM-15602 Fix for logging- only regenerate timestamp triggers on requested tables

@eileenmcnaughton Here's a PR against 4.4 as requested. Please note that we have only tested on Drupal with 4.4.6. Details of that are in the forum and jira- basically re-did the show triggers, trigger rebuild, show triggers, add a new custom field, show triggers. Both the CRM_Core_DAO change and the CRM_Contact_BAO_Contact change gave good results there compared to before the fix. I'm going to ask on the forums if anyone's willing to test against Joomla and WP, but there shouldn't be anything CMS-specific in the patch.