#1426: rose edit: fix spaced widget bug.

This fixes #1426. The problem was misuse of the 'last_value'
property across all array widgets, which happened to work
as it was always set to the actual current value, except in
the spaced_list widget.
Merge pull request #1430 from benfitzpatrick/1426.rose-edit-fix-spaced-widget-refresh

#1426: rose edit: fix spaced widget bug.