gsdx ogl: various minor optimization. 
* move most of gl states into a separate namespace. Extend it to depth/stencil/blend micro state
=> save 10,000 opengl call by frame for colin mcrae 3
* Only setup blend state of first drawbuffer
* Don't request anymore a debug context on dev/release build



git-svn-id: http://pcsx2.googlecode.com/svn/trunk@5713 96395faa-99c1-11dd-bbfe-3dabce05a288