[orca-list] Do not flat review in Gtk+ trees for now

[Joanmarie Diggs <jdiggs igalia com>]

Hey all.

In case it wasn't clear from my two responses to Cleverson, there seems
to be a regression in Gtk+ (or pango). The impact is that flat review in
any Gtk tree will cause the app with the tree to segfault. :( I have
filed this Gtk+ bug and pinged the Gtk+ accessibility developer:
https://bugzilla.gnome.org/show_bug.cgi?id=687872

Sorry and thank you for your understanding.
--joanie