Added exclusive OverrideTraceScreenRay() for ZoomTilt (which is immune to ground height variation)

-also add zoom boundary around map for Non-freemode option
-renamed some Global constant variable (cleanup thing)
-also, had to remove ZoomTilt's Horizon check because not compatible with zooming into water (y<0). Still work!
Merge pull request #3 from xponen/patch-3

Added exclusive OverrideTraceScreenRay() for ZoomTilt (which is immune t...