Removing the workspace .xccheckout file.

This file does not make much sense for this project see http://stackoverflow.com/questions/18340453/should-xccheckout-files-in-xcode5-be-ignored-under-vcs
Replacing roundf() with round() from thmath.h. 

Improves 64 bit compatibility. See http://stackoverflow.com/questions/7694948/cgfloat-round-floor-abs-and-32-64-bit-precision