More robust check before eliminating observers

Check to ensure all rows have really been removed before eliminating
observers. Also provide better tolerance of missing rows.
Fix #383: Make ColumnSet and CompoundColumns compatible with each other

This also includes a few CSS tweaks to improve the layout of the grid header
when using ColumnSet and CompoundColumns together.

Note that ColumnSet remains agnostic to any details specific to CompoundColumns.
Keyboard: Prevent errors attempting to refocus after structure change
CHANGES.md: Note CompoundColumns + ColumnSet interop
Fix a timing problem which caused an error in unit tests in IE < 9.

This sets _started to false when a list or grid is destroyed, so that
any delayed resize handlers no longer attempt to resize when the grid's
DOM is no longer relevant.
CHANGES.md: Note change to _started behavior in List#destroy
Improve accessibility support in non-Firefox

Only add tabIndex to the scroller in Firefox since setting it prevents
screen readers from seeing the table rows in other browsers.
CHANGES.md: Note non-FF a11y fix
Fix #769: OnDemandList: only add loading node when running a query
CHANGES.md: Note OnDemandList loadingMessage regression fix
Fix #751: pass cell's value to canEdit when using a shared editor
editor: canEdit unit test clean-up

* Add descriptions to assert calls
* Use edit API instead of emitting fake click events
CHANGES.md: Note editor canEdit value argument fix
Fix a problem with a failing test causing the test runner to hang

Also added another removeRow test with justCleanup left undefined.
Update version dependencies in Intern config
Add local variant for Intern config
README.md: Add directions for running tests with local Selenium
Fix #739: tree: make expand return a promise
Improve tree expand promise tests to run fully, and add rejection test
tree: Remove call to _trackError around renderQuery in expand

The call is not necessary because the call to the query inside of
renderQuery is wrapped by _trackError.

The tree-expand-promise test now verifies the error event is being generated
and I added tests for grids that do not have an implementation of renderQuery.