Fix bug with immediate conflict detection

Fix bug with immediate conflict detection

Detecting immediate conflicts for an event is
important as part of the clean up phase of
UDPOR. There was a typo that gave incorrect
results for the actual conflicts that were
detected which was resolved.

NOTE: There is still a problem with event
deletion. The issue is that previous configurations
will contain references to events which have been
deleted in the extension set which is computed
for them (ex(C)). I'm not quite sure how to
handle this at the moment...