xfixes: Allow the client to upgrade the fixes protocol version

If you say FixesQueryVersion twice we remember whatever the second version number was. With just libXfixes this isn't an issue because the request is hidden in extension setup, but libxcb-xfixes doesn't do that for you, which means the second one can lower the requested fixes version, disabling requests that the client thought it had enabled.

Paper over this by allowing the version number to be raised but not lowered. Also go ahead and delete the minor version number from the client state since xfixes doesn't have minor versions (yet, anyway).