Carlos Garnacho authored Aug 22, 2018 and Carlos Garnacho committed Sep 24, 2018

Changes in window decoration result in the window being reparented
in and out its frame. This in turn causes unmap/map events, and
XI_FocusOut if the window happened to be focused.

In order to preserve the focused window across the decoration change,
add a flag so that the focus may be restored on MapNotify.

Closes: #273