Explicitly set current border width when BS_PIXEL

When a window becomes managed, if the config specifies a pixel border
style, explicitly set the current border width so it does not change
when the container changes from tiling to floating.

fixes #1266
Merge branch 'fix-width'
Merge branch 'master' into next
Revert "Disable render-time pointer warps if asked"

This reverts commit b109b1b20dd51401dc929407453d3acdd8ff5566.

Turns out the change in behavior was unexpected by a number of users, so
let’s revert it and make those users that want this behavior configure
it explicitly.

Sorry for the back-and-forth here.
Merge branch 'revert-warp'
Merge branch 'master' into next