_StoreMixin should leverage object.set if it exists and is a function.
CHANGES.md: note Stateful support in _StoreMixin#save
CHANGES.md: demote IE8 ColumnHider note
Remove dijit/Editor test from editor test page

Trying to explicitly support Editor is more trouble than it's worth, and it's a
rather heavy widget to be including inside a grid to begin with.
Squashed commit of the following:

commit daa09d9774e3701acfc6122279d489cea804119b
Author: Ed Hager <ed.hager@gmail.com>
Date:   Wed Jun 5 10:04:16 2013 -0700

    Reformatted my last change to use tabs instead of spaces.

commit 0754088eaf74cddbaf3dd75b976316b9e63ad1f9
Author: Ed Hager <ed.hager@gmail.com>
Date:   Tue Jun 4 17:24:52 2013 -0700

    Fixed a problem in the test ordered store when an item was placed at the end of the list and the options.before property was missing.