Borders don't follow window movement

[peppy]

Reproduction:

• Set window border to >0px
• Swap windows using (in the example yabai -m window --swap west)
• Border's "shadow"(?) portion doesn't follow the movement and sticks to the wrong window.

In the example I've made the width very thick to better show the issue. I do two swaps west then one swap east.

[koekeishiya]

What the heck, borders are not supposed to have shadows. Guess I never noticed because I run with window_shadow off and that also removed the shadow of the border window created by yabai, or maybe I just never noticed due to using a rather small width.

[peppy]

The weird part is, it still happens with window_shadow turned off (the active border doesn't have a shadow, but the "ghost" one does:

[koekeishiya]

I misspoke earlier. Borders created by yabai are not affected by the window_shadow setting. Made a change to master that explicitly disables the shadow when the border window is created, and that seemed to fix the issue for me.

[peppy]

Tested head, works perfectly. Thanks!