once fires off callbacks one time,
condition lets you plug in an a==b, or method that returns a true/false;
trippedby lets us plug in things like $TypeMasks::PlayerObjectType ( ac39577543/Engine/source/T3D/gameFunctions.cpp (L658) ) so that *only* players can trigger it
1- corrects onleavetrigger for deletions
2-adds a testObjects to trip onenter when creating or moving a trigger itself so that that will list objects already there as opposed to only going off when something moves into it
Specifically:
* Made update bits constants protected so that derived classes can
use them - especially NextFreeMask! IIRC, most classes make these
constants public, though there's no real reason to.
* Made potentialEnterObject virtual so that derived classes can
substitute their own logic.
