tests: Fixed testOpFeatureMatrixCache.py
tests: When opening a file to check an exported result, close the file before exit.
BlockwiseFileset: Not tested (and therefore not supported) on Windows and Darwin.
tests: skip RESTfulBlockwiseFileset tests on mac and windows.
submodules: Updated dvidclient
tests: More cleanup of data checking operators before exit.
OpTrainRandomForestBlocked: If there aren't enough labels to train with, return None.
OpSlicedBlockedArrayCache: Don't mark everything dirty if the blockshape is dirty.  That's an error anyway.
OpFeatureMatrixCache: When handling dirty feature rois, only mark those blocks dirty that are already in the cache.
roi utilities: determineBlockShape(): Round when converting each dim to an int (results in more intuitive block shapes)
Merge branch 'master' into OpLabelVolume-optimization
make sure the 'right' blockedarray version is used