Xi: check for Use permission on the device in SetClientPointer().

Presumably, some intelligent, XI2-aware management app will be calling
XISetClientPointer on behalf of other clients; this check makes sure
the target client has permission on the device.

Requires changing the prototype to return status code instead of Bool.

Signed-off-by: Eamon Walsh <ewalsh@tycho.nsa.gov>
Acked-by: Peter Hutterer <peter.hutterer@who-t.net>

include/dix.h

@@ -485,7 +485,7 @@ extern _X_EXPORT int TryClientEvents(
 
 extern _X_EXPORT void WindowsRestructured(void);
 
-extern Bool SetClientPointer(
+extern int SetClientPointer(
         ClientPtr /* client */,
         DeviceIntPtr /* device */);