Comments.
BlockwiseFileset: Added isBlockLocked()
Merge branch 'master' of ssh://github.com/ilastik/lazyflow
OperatorWrapper supports len()
OpArrayCache: Added CleanBlocks output slot and also fixed a bug in setInSlot().
OpCompressedCache and OpCachedLabelImage support CleanBlocks output slot and setInSlot() for forcing values into the cache.