This code was constantly failing to find the current files user as
the form of the "owner" attribute didn't match the internal list.
Also, as a consequence of this the user list didn't match the old
one so we keep re-creating it all the time.

We fix this by being much more explicit in what we store in the
model columns:
0 - the display name
1 - the return value from nautilus_get_user_names()
2 - the actual username (not real name)