Update rcguard.php

Makes time comparison always based on the DBA time (my DBA is currently mysql for me).

PHP timezone and the DBA timezone can be different.
For the DBA, the function NOW() returns a local datetime.
For PHP, the function date() returns also a local datetime.

When PHP timezone and DBA timezone was not the same (example : GMT for PHP and Europe/Paris for DBA), comparison was always wrong.

Warming : I didn't try my code for persistent login but I guest it's OK.
Merge pull request #7 from Yappli/master

Bug fix when PHP and DBA don't have the same timezone setting