The POINTER_SCREEN flag must be set explicitly for XTest core events to avoid
out-of-range events when the lastSlave was an SD with an explicit axis range.
Device events sent through XTest don't need this flag, they are expected to be
in the valuator range of the device anyway.
Red Hat Bug 490984 <https://bugzilla.redhat.com/show_bug.cgi?id=490984>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>