BlockwiseFileset: Added sub_block_shape setting.
BlockwiseFileset: Added a debug feature: dataset description file is written to each block directory for debugging purposes.
Corrected a debug log message.
OpFilterLabels: Fixed logic for the 'shortcut' path to make sure that the max size is considered if necessary, even if minsize is 0.
BlockwiseFileset: Relax constraint on sub_block_shape to allow it not to divide evenly into the block shape IF the block shape spans the entire dataset shape for the dimension in question.
BigRequestStreamer: Actually respect batchSize parameter.
BlockwiseFileset: Support arrays with dtype=object (stored as arrays of pickle strings)
memory management: Remove lock order inversion from _allocateCache(), but others exist.  Also, I'm not sure if what I did in this commit is okay.