First attempt at TreeView typeahead

[Jonathan Blandford <jrb redhat com>]

Here's a first pass at implementing typeahead in the GtkTreeView.  It's
not done yet and is not ready to be committed.  I really like how much
nicer it is making the file chooser, though.  I'd love it if a few
people could try it out and send back any issues to me.  The two big
issues I know about are:

 * The flickering entry in the corner
 * input-methods not fully working yet when the first key is pressed

The patch is available at:

  http://www.gnome.org/~jrb/files/treeview-typeahead-0.1.patch

Thanks,
-Jonathan