Fix voglgen_make_inc to only run when needed, rather than every build.
Merge branch 'master' of https://github.com/ValveSoftware/vogl
move voglcommon back to the NOT WIN32 group, not ready for windows yet.
Convert tabs->spaces in voglgen/CMakeLists.txt
Merge pull request #51 from vMcJohn/master

codegen now only runs when needed