2014-11-07-22.16.53: src/lib/x-kit/widget/gui/guiboss-imp.pkg: Topwindow_Info: Replace   running_gui: Ref(Null_Or(gt::Running_Gui))   field with   backing_pixmap: Ref(Null_Or(gt::Backing_Pixmap))   field because with popups having their own Running_Gui instances we can no longer think in terms of at most one Running_Gui per topwindow.   src/lib/x-kit/widget/gui/guiboss-imp.pkg: Backing_Pixmap:  TOPWINDOW_PIXMAP:  Add a   running_gui: Ref(Null_Or(Running_Gui))  field because we have established Backing_Pixmap as the recursive datastructure tracking the popup parent/child tree, so this is the natural place now for the Running_Gui record for each popup to live.