classifiers: Factories must implement __eq__ so they can be used in a MetaDict.
MetaDict: Implemented __eq__ and __ne__
operator: setup optimization: Don't call _changed() for slots whose metadata didn't actually change.
OpSubRegion: If Roi and Input dimensionality are mismatched, just set Output.NOTREADY, don't raise an error.
OpFormattedDataExport: Leave SubRegion operator disconnected if the roi dimensionality is mismatched.
dense caches: If Input and blockshape dimensionality are mismatched, simply remain NOTREADY.
OpCompressedCache: It is no longer an error to reconfigure the blockshape more than once, but it IS an error to do so while execute() is being called simultaneously in a different thread.
OpFeatureMatrixCache: Discard cache whenever setupOutputs is called again.
OpValueCache: Become dirty when input becomes unready.
docstring.
feature matrix caches: Mark output dirty after setupOutputs()
Operator: When an input becomes unready, set all operator outputs to unready, including subslots.
OpMultiArraySlicer2: As soon as the input becomes unready, resize the output slot to nothing.
Slot._changed(): Use ready() instead of meta._ready to determine if the ready-state has changed.  Should be more consistent behavior for multislots.
Revert "Operator: When an input becomes unready, set all operator outputs to unready, including subslots."

This reverts commit d40f6897462529dc4fece406c810834127f9a803.
testOpMultiArraySlicer2: Removed unecessary dirty test in testReshape
Merge branch 'dimensionality-fix'
These changes were necessary to deal with ilastik/ilastik#941 (see corresponding changes in ilastik/ilastik, too)