GNOME/nautilus: set default to browser mode

[Me]

>>>
>>> Does anyone have an opinion whether we should make this change
>>> worldwide? Or make it an option in the build configuration for
>>> olpc-os-builder users? (in the 2nd case, which would be the default?)
>>>
>>> In all cases, the user can change preferences later.
>>>

As of GNOME 2.30 nautilus defaults to browser mode.  Even though we
don't ship with the most recent distro and associated application
versions, it is probably worth consideration to follow their most
recent usability decisions where possible.  Adopting these changes and
not exposing the user base to an environment we know will most likely
change to follow upstream in the next release will only emphasize the
goal of keeping the interface simple and consistent.

Jon