This patch adds more robust checks for WGL_ARB_pixel_format and
WGL_ARB_multisample before using the relevant extensions, and adds
checks whether Wgl.Arb.ChoosePixelFormat() returns a valid pixel format
before trying to use it (thanks to Repetier for catching this edge
case.)
Additionally, the ChoosePixelFormatPFD code-path now heavily penalizes
single-buffered modes when the user requests a double-buffered mode.
Affects issues #42 and #45
bdfcf43e0b