Mouse pointer is off

[gajop]

http://i.imgur.com/R6UtiWC.png

[aeonios]

mouse pointer snaps to the terrain using a not-so-precise intersection algorithm. If you can do better then make a PR. :| I've tried several things and haven't gotten particularly good results. I don't really want it to point directly at the coords under the pointer either, since that prevents you from painting the backs of hills and can lead to painting surfaces that are far away by accident.