exact triggers: jumppads, teleporters and race checkpoints now work EXACTLY as

exact triggers: jumppads, teleporters and race checkpoints now work EXACTLY as
made in the map editor (not as bbox any more). This change might be desirable
on other entity types too.

Usage:

- In the spawn functions, call EXACTTRIGGER_INIT; instead of InitTrigger();
- In the touch function, first do the classname checks, then call EXACTTRIGGER_TOUCH;
  (this will abort the touch function if it is a bad touch)

git-svn-id: svn://svn.icculus.org/nexuiz/trunk@4142 f962a42d-fe04-0410-a3ab-8c8b0445ebaa