specs: More accurately describe PIXELFORMATDESCRIPTOR members.
specs: More accurately describe wglCopyContext function.
glretrace: Warn if ChoosePixelFormat returns GDI software implementation.

By some mysterious reason, I've started to see this happening on one
machine, even though there are hardware accelerated pixel formats
available.
glretrace: Cleanup ChoosePixelFormat arguments.

- order member assignments
- cColorBits should not include alpha
- cRedBits/cGreenBits/cBlueBits are ignored

See http://msdn.microsoft.com/en-us/library/windows/desktop/dd318284.aspx
glretrace: Don't request alpha bits pixel formats on Windows.

To prevent ChoosePixelFormat from picking up software pixel formats.