dix: change the filters to be per-device.

If we have one global filter, one pointer may change the filter value and
affect another pointer.

Reproduceable effect:
blackbox and xterm, start dragging xterm then click anywhere with the other
pointer (attached to different masterd device!).  The button release resets
the filter[Motion_Filter(button)] value, thus stopping dragging and no event
is sent to the client anymore.
Having the filters set per device gets around this.

include/dix.h

@@ -345,6 +345,7 @@ extern void SetVendorString(char *string);
 /* events.c */
 
 extern void SetMaskForEvent(
+    int /* deviceid */,
     Mask /* mask */,
     int /* event */);