FileLock: purge() returns a bool to indicate whether or not a lockfile was found.
blockwiseFileset: Use lockfiles to ensure that there cannot be simultaneous access to a file that is being written.
BlockwiseFileset: Assert if we can't get a lock on a file we want to write.  Multiple processes shouldn't be competing for the same files.
FileLock: Instead of leaving the lockfile empty, give it some contents that might be useful while debugging.
BlockwiseFileset: Avoid AttributeError in __del__.
request: Old implementation has a few definitions to support forwards compatibility, for easy switching back and forth between implementations.
request_rewrite: After the callback signals are fired, clean the callback lists to free references to bound args quickly.
BigRequestStreamer: Cleanup an unused variable.
RoiRequestBatch: Fixed a memory leak and added a unit test.
RoiRequestBatch: Now works for both old and new request backends.
request: clean() removes children and result.
request: result is now a property with various asserts.
roiRequestBatch: Fixed the memory leak for real this time.  Improved the test case to be more general.
Remove assignments to req.result
request: wait() asserts if the request has already been cleaned.
request: Added block(), which waits but doesn't return a result.
roiRequestBatch: Clean each request as soon as it is finished and signaled.
request: Fixed a crash in wait()