Fix selected items in content view when filtering

Reported by NFI users, can be reproduced actually on {{demo.nuxeo.com }}

• first I navigate to > Default domain > Workspaces > IT Department
• Now the content view displays 5 folders (expertise center, it mailbox, maintenance, projects, reporting).
• Now in the field above the content view next to the Filter button I write expertise and click on filter.
• The content view shows only the expertise center folder.
• I select the checkbox in this folder.
• The buttons copy, add to worklist and delete become clickable
• now I click clear filter
• The buttons are still cickable however, no checkbox is selected.
• When I click copy and after that I click paste you can see it pasted the folder I selected in the filter before.

So it remembers which documents are selected in the filter, but when you clear the filter the checkboxes are beeing emptied.

I use Google Chrome as browser, but it also happens in IE8.