Push the rrule_event_overlaps function into the 8.1 compatibility functions.
Push the rrule_event_overlaps function into the 8.1 compatibility functions.

lkraav/davical-rss-feature-branch,lkraav/davical-rss-feature-branch,lkraav/davical-rss-feature-branch,lkraav/davical-rss-feature-branch