Make wfSuppressWarnings kill E_STRICT in PHP 5.4+

Since PHP 5.4+ E_STRICT is now included in E_ALL. Hence
wfSuppressWarnings was not filtering E_STRICT.

There was some complaints on project:support_desk about
timezone warnings popping up. See also bug 43092

Change-Id: Ie1ace158dac1733e6b2b2c1d533004d9bcab8c80