GL3.0 Conditional rendering

[Laar]

Implement conditional rendering,
OpenGL spec sec. 2.14

[Laar]

I've implemented it in laar@5237b3ec294d20cafe38fd4c307a9e59e413e761. Though it's untested and it extracts all the QueryObject code from the PerFragment module to it's own.

[Laar]

Tested, and it works.

[Laar]

Has been merged in #27.