support event 5.x-2.*

That's the error I'm getting, when submitting a sign-up or running cron with event 5.x-2.x-dev installed:

Fatal error: Cannot redeclare event_is_dst() (previously declared in /xxxxxxx/sites/all/modules/event/event.module:2356) in //xxxxxxx/sites/all/modules/event/event_timezones.inc on line 187

I understand, that this is a development version, but still...