better handling for exceptions

Currently if there is an exception you get something like:

Fatal error: Uncaught exception 'Exception' with message 'Error while mailing. Postmark returned HTTP code 422 with message "Sender signature not found for email."' in /vol/drupal/6_drupal/sites/all/modules/postmark/includes/Postmark.php:276 Stack trace: #0 /vol/drupal/6_drupal/sites/all/modules/postmark/includes/postmark.drupal.inc(66): Mail_Postmark->send() #1 /vol/drupal/6_drupal/sites/all/modules/postmark/postmark.module(46): postmark_send(Array) #2 /vol/drupal/6_drupal/includes/mail.inc(177): drupal_mail_wrapper(Array) #3 /vol/drupal/6_drupal/includes/mail.inc(130): drupal_mail_send(Array) #4 /vol/drupal/6_drupal/sites/all/modules/project_issue/includes/mail.inc(278): drupal_mail('project_issue', 'project_issue_u...', 'ezra@example.com......', Object(stdClass), Array, '"ben (Project -...') #5 /vol/drupal/6_drupal/sites/all/modules/project_issue/project_issue.module(856): project_mail_notify('4217') #6 [internal function]: project_issue_exit('http://project....') #7 /vol/drupal/6_drupal/includes/module.inc(483): call_user in /vol/drupal/6_drupal/sites/all/modules/postmark/includes/Postmark.php on line 276

It would be nice if the module could catch exceptions, log them to watchdog as php errors, and allow the page processing to continue.