Deferred trigger queue to disk

All this does is put all the trigger events given to it after a certain
number out to disk in DeferredTriggerAddEvent; then read them as
necessary in DeferredTriggerInvokeExec.
The certain number after which it moves to disk is currently, &
arbiterily, 100000 defined by this line in trigger.h:
#define max_deferred_trigger_mem_queue 100000
It has passed the regression checks on Linux (RH9ish) and cygwin.
Also include is a quick test script I used
This is my first patch of any size so please review carefully.
regards,
- Stuart