My b2evolution Version: 4.1.x

My hosting provider has upgraded from PHP 5.2 to PHP 5.3.10, I am now seeing lots of these errors in b2evo:

Warning: date() [function.date]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'Europe/London' for 'BST/1.0/DST' instead in /home/robertc/public_html/b2evo/inc/_core/_misc.funcs.php on line 1240

I'm assuming an easy fix is to call date_default_timezone_set() in one of the initialization routines but haven't investigated further than that. Where would be the best place to put it? What alternative approaches are there?

Rob