WIP: some fixes for a buggy auto filter test (but it is still incorrect, needs to use unique primes for each factor). Also got a buggy implementation of auto-filtering - only running the filter on the topmost node.
Simplified a test for auto filters and updated documentation after realising there are some fundamental limitations in the auto filter concept. Still have a genuine bug to fix, though - there are far too few test cases generated in what is now a part-manually verified smoke test....
Caulk of this branch for now - removed buggy implementation of auto-filters, what is left now fails the tests. Need to think about how to traverse the node tree in the auto-filter case - the current code makes a point of removing singleton test variable values, this gets in the way of autofilter support.