multisample context creation: Windows version.

git-svn-id: https://www.libavg.de/svn/trunk/libavg@9537 44470bb9-56e9-0310-a0f8-c586564d3dc6
multisample fix for mac.

git-svn-id: https://www.libavg.de/svn/trunk/libavg@9538 44470bb9-56e9-0310-a0f8-c586564d3dc6