Fixup misused glXChooseFBCOnfig: GLX_VISUAL_ID is ignored.

This is visible only is bare Window XID is passed to ctor,
and glXQueryDrawable fails (happens on Mesa). We cannot choose
fbconfig by VISUAL_ID (it's ignored according to spec), so
iterate through all FBConfigs and match manually by visual id.
Return proper stereo and double buffer flags for GLX surface (always returned true)