Correct bug in test - use the encoded test variable level indices, rather than the ones passed explicitly to the filter - this matches the cross product used to set the test expectations in 'TestCoverageOfNCombinationsOfVariableLevelsInFinalResultsIsComplete'.
Correct typo causing obvious test failure - now got *another* test failure in the same test.
Fix bug in test by using consistent zero-relative test variable level encoded levels - means that the change introduced in commit 506 for the fundamental filtering criterion now applies correctly. Still have two test failures outstanding.
Trivial reformatting.
Correct errors and sloppiness in tests:-
1. Must ensure that trees have no prunable pieces in addition to switching off explicit subtree permutation when checking the test variable indices passed to filters.
2. Make sure that duplicated test levels have encoded level indices that start off from zero.
3. Use the test variable index passed in to the filter in the test-supplied filter - the expectations now work with zero-relative indices, so it's safe (and better in the case of duplicated levels) to do so.
Improve implementation of Node.CombinedFilter - easier to understand.