This reverts commit c15f7c85.

This is needed for OS X to signal the NSApp that
we are ready to receive events. This needs to be
done after the main gedit window has been created
because those events contain things like OpenFile

Try to address some question raisead on IRC.

Block the selection changed callback while refresing the list.

Track the selection with selection::changed instead of the cursor.

Gtk started to emit cursor-changed when the treeview is destroyed. I am
not sure if it is a Gtk bug or if it is intentional, but we should check
for errors returned by the getter function.