OpExportSlot: HDR export format requires exactly 3 channels.
OpExportSlot: TIFF export doesn't support signed byte.
Fixes ilastik/ilastik#585
OpExportSlot: More format validity checks.
Fixes ilastik/ilastik#588
OpExportSlot: Added comment linking to vigra issue tracker.
OpFormattedDataExport: Configure internal OpReorderAxes after the renormalization operator (configure all operators in same order as the pipeline)
OpNpyWriter: Added a warning explaining that npy export isn't really properly lazy.
correctly deal with no forests in prediction
Request: Added convenience functions for checking the cancellation status of the current request.
RequestLock: Now aware of cancelled requests.  Immediately raises a cancellation exception if the current request was cancelled while it waited for the lock.
request.py: Added a special request-aware condition variable class called SimpleRequestCondition (with a test).
I'm going to revert this in my next commit because it turns out that threading.Condition works fine with RequestLocks, but I want this code committed for posterity.
Revert "request.py: Added a special request-aware condition variable class called SimpleRequestCondition (with a test)."

This reverts commit e6fda6988c2c80e721b301506fbd479e3a90b312.
RoiRequestBatch: Simplified and improved the implementation using a condition variable to manage  request launching and completion.
This should also fix a critical issue that prevented spawned requests from being cancelled properly, and more naturally avoids excessive memory usage than the previous implementation.
tests: testRoiRequestBatch: Cleaned up logging.
Slot: If a value slot is about to assert, check to see if the current request has been cancelled.
tests: request: Added a test demostrating how to use threading.Condition with a RequestLock()
rechecked patchification
extended training
fixed really annoying bug
added obvious comment
simplifications, training script stuff