make event overlay wireup synchronous for ipc:// and tcp://

This addresses the problem of tests starting before events can be received, and then losing something imporant to the test.  Initial events can still be lost, but any command will not be run until all members of the session are fully wired up.

This is a better solution than the 250ms sleep we had added to work around spurious test failures.

This has no effect on epgm:// wireup which should not suffer from this problem (I think!)

Fixes issue #38