Method GetChangesets() only for tfs2008 to avoid bad changesets returned when getting by lots

Expected fix #642
Try without the Retry.Do()
Correct the double fetch of changesets
Directly as if "Is2008OrOlder"
Merge pull request #646 from pmiossec/fix_wrong_changesets_order_tfs2008

Method GetChangesets() only for tfs2008 to avoid bad changesets returned...