Dmrefresh

This PR fixes the refresh issue see http://trac.openmicroscopy.org.uk/ome/ticket/10006

To test
 * Tag a dataset with images.
 * Tag a project containing a dataset with images.
 * Go to the Tags tab
 * Expand the tagged dataset
 * Expand the tagged project and the dataset contained in the project
 * Click refresh
 * The error described above should not be present.
 * The datasets should be expanded.

see @mtbc
Set-up screenshot
![dmrefresh-setup](https://f.cloud.github.com/assets/1022396/1180929/602427da-21ff-11e3-9ced-2cecd9fd7700.png)