Because cursor warping was the default behaviour in seat_set_focus,
there may be cases where we may have been warping the cursor
unintentionally. This patch removes cursor warping from seat_set_focus
and only does it in the focus command. This is managed by a static
function in focus.c.
To know whether to warp or not, we need to know which node had focus
previously. To keep track of this easily, seat->prev_focus has been
introduced and is set to the previous in seat_set_focus.
24a90e5d86