In co-op termination, extend EventWaitHandle to give this an indefinite lifetime in order to avoid a later RemotingException if scripts are being loaded into their own domains.

This is necessary because XEngineScriptBase now retains a reference to an EventWaitHandle when co-op termination is active.
Aims to address http://opensimulator.org/mantis/view.php?id=6634
Merge branch 'master' of ssh://opensimulator.org/var/git/opensim