[fix] resize should now preserve surrounding container's dimensions
[fix] resize should now preserve surrounding container's dimensions

- prior to this modification, the requested pixels were added/removed
  to both edges of the modified container. To preserve sizes,
  only half the pixels should be added/removed to each edge.

sleep-walker/sway,1ace/sway,1ace/sway,sleep-walker/sway,SirCmpwn/sway,mikkeloscar/sway,ascent12/sway,1ace/sway,taiyu-len/sway,ascent12/sway,4e554c4c/sway,4e554c4c/sway,johalun/sway,taiyu-len/sway,ascent12/sway,ptMuta/sway,taiyu-len/sway,mikkeloscar/sway