Check publish workflow dates towards the document we are testing

This commit solves the issue https://github.com/symfony-cmf/symfony-cmf/issues/172 for SimpleCmsBundle.
The test seems to show another problem: fails because after the flush on line 48 the value of $data['publishStartDate'] and $data['publishEndDate'] is changed to the day before.
Merge pull request #76 from dicorato/patch-1

Check publish workflow dates towards the document we are testing