Make tests for flaw-gl

[quyse]

Tests may render some test scenes and compare results with reference rendering.
Things to test:

• Different sets of enabled capabilities: support for uniform buffers, vertex attrib binding, texture storage
• Different instancing modes
• Exporting and using binary programs

[quyse]

Apparently manual setting uniforms (GL_ARB_uniform_buffer_object is disabled) is broken right now.

[quyse]

Disabling GL_ARB_vertex_attrib_binding doesn't work either :(

[quyse]

As of 1e12924, manual uniforms are fixed, manual attributes are partially fixed (they work for webgl, but fails for opengl for some reason).

[quyse]

77a95b5, manual attributes are fixed: added correct handling of vertex array object extension.