Fixed bug with not-removed events
Problem: With Horizon the semantics of cScheduler::getNextEvent() and
cSimulator::doOneEvent() where changed. Without Horiozn, getNextEvent()
peeked the event in the FES, and doOneEvent() removed it. This was
changed for Horizon, but the cParsimScheduler::getNextEvent() function
Solution: Reverted the semantics back to the stock OMNeT++ semantics.
This introduces a problem with the cEEFScheduler since the EEF scheduler
needs to pick a bunch of events from the FES and select one. This was
fixed by putting the selected event back into the heap in
cEEFScheduler::getNextEvent(). I prefered this solution since the
changed semantics would also break the TkEnv.