Fix more calls to XQueryPointer for MPX

Fix more calls to XQueryPointer for MPX

* src/xterm.c (x_dnd_begin_drag_and_drop): Set DND devices to -1
if XI2 is not supported on the given display.
(x_query_pointer): Make wrapper around x_query_pointer_1.
(x_query_pointer_1): Split off most of x_query_pointer to this
function.  Allow a specific client pointer to be specified.
(x_dnd_update_tooltip_now, x_dnd_update_state): Use
x_query_pointer_1 with the right device instead of
XQueryPointer.