Data test updates (rebased onto dev_4_4)

Primarily this allows multiple threads to be used when running the data tests.  See http://hudson.openmicroscopy.org.uk/view/All/job/BIOFORMATS-full-repository-stable/ and http://hudson.openmicroscopy.org.uk/view/All/job/BIOFORMATS-repo-stable-for-debugging/

This includes most of the commits from gh-643, minus merge commits and Memoizer-related things.