Improved underscore method validation

Introduces some complicated function-wrapping
to try to make it harder for players to call
underscore methods on map in their code (i.e.
methods they shouldn't have access to anyway)
minor
beginning to validate callbacks
lots of fixes to validation -- primarily getting exits and lvl15 to work
callback validation - getting dynamic objs, lvl7 to work
adding checks to unexposed player and dynamicObject methods
fixing lvl17 by wrapping player._moveTo in teleporter def
getting ready for big merge
Merge branch 'better_underscore_checking' of github.com:AlexNisnevich/untrusted into better_underscore_checking
Merge pull request #236 from AlexNisnevich/better_underscore_checking

Better underscore checking