Two nested scroll views were fighing with each other. The reason isn't
particularly important and has to do with some silliness involving
StAdjustment. The visible effect was that scrolling up and down when
in a summary item view would appear to be glitchy, and sometimes not
work at all.
To fix, make sure that the scroll view we don't care about is disabled
when in a summary mode.
https://bugzilla.gnome.org/show_bug.cgi?id=661615
