Remove unused (and immediate mode) GRAPHICS_GL2::DrawBox.
Cache selected texture unit, saves about 30% call time per simple single textured object.  GLSTATEMANAGER doesn't take texture unit into account, only enables/disables first unit, should be fixed eventually.
Style: Spelling fix in comment.
Remove unused REDNER_INPUT_SCENE::SelectAppropriateShader and redundant GetCull check.
RENDER_INPUT_SCENE move DrawVertexArray code into a function, move GL_LINE_SMOOTH setup to BeginScene.