[BUGFIX] #5178 Use time() instead of mktime()

mktime() without any parameters causes PHP strict warnings,
starting with PHP 5.1.

Change-Id: Ie23d67a30c5c95fa902660c5c05fbb92d36f5b0e
Reviewed-on: http://review.typo3.org/34700
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>