Improved Checkbox editor ValueChanged behavior.

Checkbox editor was firing onCellChange event even when there was no change. This fixes that behavior and also returns a boolean on serialzeValue instead of the previous "checked" or undefined.
Remove usage on $.browser for jquery 1.9.0

jquery 1.9 has removed support for $.browser, use navigator.userAgent
instead
Merge pull request #543 from pzgz/jquery.1.9.0.fix

Remove usage on $.browser for jquery 1.9.0
incorporated suggestions by mleibman
Merge pull request #542 from wilcley/master

Checkbox editor ValueChanged event behavior fix
Optimize DataView flattenGroupedRows().
Merge remote-tracking branch 'upstream/master'

Conflicts:
	slick.grid.js