Comment 3 for bug 1669103

The change was intended and requested by me while reviewing the merged branch. My arguments why I wanted this change:
- Consistency with the behavior of other dialogs. The construction and enhance* dialogs also stay open. That is, they are opened when construction/enhancing starts and open the matching building dialog when done.
- When dismantling a building for its building space it is useful to know when its done (okay, a weak argument).
- The window can be closed with a right click so (in my opinion) it is no big problem when not needed.

To change this back: The relevant changes when adding it were:
https://bazaar.launchpad.net/~widelands-dev/widelands/notifications_buildingwindows/revision/8153/src/logic/player.cc

* I also take the blame for opening the "currently enhancing" window. ;-)