Cached tooltip windows were preventing the automatic event loop shutdown.
It's not like we were gaining much by caching these anyway, since we only
cached the GWindow, not anything on the WindowServer side.
This behavior is the new opt-out default. If you don't want your app to exit
when the last GWindow is destroyed, call this:
- void GApplication::set_quit_set_quit_when_last_window_deleted(bool)
Also renamed "windows()" to "reified_windows" in GWindow.cpp to reflect that
it only contains GWindows that have a server-side representation. :^)
