Revamped Threads tests to only generate noise at leaves.
Revamped Threads tests to only generate noise at leaves.

This was done because it both makes the runtime faster
and the code simpler and also because the noise is
generated at positions in the search tree which are
probably more likely to result in interesting
behaviors which can uncover the existence of errors.
gcross/LogicGrowsOnTrees,gcross/LogicGrowsOnTrees