Split ChangeMasterDeviceClasses into an extra XISendDeviceChangedEvent that
assembles the XI2 wire event for the DeviceChanged event. Re-use this when
detaching the last SD.

Not quite perfect yet, we still copy the device classes from the slave now
rather than from the data we had when the event occured. But it's a start.

(We can now unexport SizeDeviceInfo and CopySwapDevices, not needed anymore)

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>