Optimized the `getTileOffset*` function by ~20% !
Optimized the `getTileOffset*` function by ~20% !

http://jsperf.com/indexed-array-access-versus-cached
(Should help draw stuff a little bit faster when using dynamic
rendering)

MarkoIvanetic/melonJS,gopalindians/melonJS,TukekeSoft/melonJS,rlugojr/melonJS,Smoss/Enoru-eco,srbala/melonJS,melonjs/melonJS,rlugojr/melonJS,MarkoIvanetic/melonJS,TukekeSoft/melonJS,rlugojr/melonJS,gopalindians/melonJS,TukekeSoft/melonJS,melonjs/melonJS,srbala/melonJS,srbala/melonJS,gopalindians/melonJS,Smoss/Enoru-eco