- Introduce warp_to static variable in x.c that stores the coordinates
to warp to as a Rect.
- Add x_set_warp_to function to set this variable. Use in _tree_next,
workspace_show, and con_move_to_workspace.
- In x_push_chanages, if warp_to is set, then call xcb_warp_pointer_rect
and then reset it to NULL.
This fixes all know bugs for pointer warping for me.