JS: introduce a threadlocal eventmanager reference that cen be read lock-free

The currentEVT is set by the Process when waking each time and can thus be read
only be the current Process without a synchronized block...but this is OK as we
only want the current process to use it.

Signed-off-by: Harvey Harrison <harvey.harrison@ausenco.com>
JS: fix for broken killEvent implementation that is leaking Processes

The event was being removed, but any held threads were not being released.

Signed-off-by: Harvey Harrison <harvey.harrison@ausenco.com>