Various fixes

Hi,

The round(...) fix in platform.h/c isn't necessary when using Visual C++ 2013 RC, and instead causes a redefinition-error, so I changed it to reflect this. I also fixed some outstanding issues from the Google Code-project, and added a workaround to a GLUT-bug which affected demo-cube for me. See commits for more details.

Everything compiles and seems to work as expected, but I've only tested with VC2013RC.

Cheers,
Christian