Fixed bug #55397: Comparsion of incomplete DateTime causes SIGSEGV.
Add a timestamp to the mail log.

This patch is loosely based on the one in bug #52126 but instead of
using a UNIX timestamp it uses the date format also being used by
error_log et al.
Add unit test for mail.log ini setting.
Merge branch 'PHP-5.5'
Merge branch 'PHP-5.3' into PHP-5.4
Merge branch 'PHP-5.4' into PHP-5.5
Merge branch 'PHP-5.5'
Merge branch 'master' of git.php.net:/php-src