Changes

Fix bug #459 NV/Win7 PDF/caps selection

Scenario
  - NV / Win7 driver version 266.58's
  - Caps: on-scr, rgba 8/8/8/0, accum-rgba 0/0/0/0, dp/st/ms: 16/8/0, dbl, mono

The above 'wglChoosePixelFormatARB' impl returns an array of pixelformats,
where the 1st entry is not hardware accelerated!
This should be considered a bug in NV's driver, since the array should return
a list ordered from 'best' to 'worst'.

Workaround trying explicit hw acceleration 1st, then generic, then software.