Don't create another context in Win32Context.attach() if the sub-class (Win32ARBContext) already created one
Don't create another context in Win32Context.attach() if the sub-class (Win32ARBContext) already created one

xshotD/pyglet,cledio66/pyglet,mpasternak/pyglet-fix-issue-518-522,mpasternak/michaldtz-fixes-518-522,odyaka341/pyglet,Alwnikrotikz/pyglet,gdkar/pyglet,google-code-export/pyglet,Austin503/pyglet,google-code-export/pyglet,cledio66/pyglet,Austin503/pyglet,arifgursel/pyglet,cledio66/pyglet,mpasternak/michaldtz-fix-552,xshotD/pyglet,arifgursel/pyglet,shaileshgoogler/pyglet,Alwnikrotikz/pyglet,mpasternak/michaldtz-fix-552,qbektrix/pyglet,gdkar/pyglet,mpasternak/pyglet-fix-issue-552,Austin503/pyglet,mpasternak/pyglet-fix-issue-518-522,cledio66/pyglet,kmonsoor/pyglet,mpasternak/pyglet-fix-issue-518-522,Alwnikrotikz/pyglet,mpasternak/pyglet-fix-issue-552,arifgursel/pyglet,qbektrix/pyglet,mpasternak/michaldtz-fix-552,xshotD/pyglet,kmonsoor/pyglet,gdkar/pyglet,Austin503/pyglet,Alwnikrotikz/pyglet,qbektrix/pyglet,xshotD/pyglet,kmonsoor/pyglet,cledio66/pyglet,arifgursel/pyglet,mpasternak/pyglet-fix-issue-552,gdkar/pyglet,qbektrix/pyglet,mpasternak/michaldtz-fix-552,mpasternak/michaldtz-fixes-518-522,odyaka341/pyglet,mpasternak/pyglet-fix-issue-552,mpasternak/michaldtz-fixes-518-522,google-code-export/pyglet,google-code-export/pyglet,mpasternak/michaldtz-fixes-518-522,qbektrix/pyglet,odyaka341/pyglet,shaileshgoogler/pyglet,google-code-export/pyglet,shaileshgoogler/pyglet,kmonsoor/pyglet,odyaka341/pyglet,Austin503/pyglet,gdkar/pyglet,odyaka341/pyglet,xshotD/pyglet,shaileshgoogler/pyglet,shaileshgoogler/pyglet,mpasternak/pyglet-fix-issue-518-522,Alwnikrotikz/pyglet,kmonsoor/pyglet,arifgursel/pyglet