persistent tree layout in list view

[John Keller <gnome johnkeller com>]

As with my previous email (selection/"keyboardability" issues), there's
a core functionality in Nautilus that I think might merit a refinement.

Since Nautilus is being positioned as more of a power-user's tool, and
now defaults upstream to opening browser windows, I'd expect that list
view might become all the more popular.

For several versions of Nautilus, the list view has allowed the user to
"unfold" folders and view their contents, without navigating to them.
This is similar to Apple's Finder view, with the exception that the
state of the folded/unfolded folders is not saved.

There is a bug which was filed last year, but relates to persistence
within a single window:
  https://bugzilla.gnome.org/show_bug.cgi?id=586067

I propose that this could be extended to a more permanent solution, with
state saved to disk as is done with emblems (see the bug for my suggestion).

Looking forward to any comments, insights, and maybe even patches. :-)

- John