Add necessary hooks for Linuxolator to see exec/exit, and thread destruction. IMO this is how it should have been done from the start.
Note that for thread destruction sysent hook, the replacement of the existing eventhandler is not equivalent: call is done much earlier while thread is still attached to the process. This is done so that p_sysent is still available, and in principle it should provide more context information to the hook, but for now it is unused since only linuxolator uses it. Also, process lock is owned there.