This enable synapser users to upload large file without running into Cstack problem.
Validated that single threaded upload worked.
tested w/ a 80MB file and saw that the progress updated sequentially in 8MB chunks when synapseclient.config.single_threaded=True and that it updated in larger chunks when synapseclient.config.single_threaded=False depending on the timing of the threads.
I have to note that the performance hit when uploading in single thread mode is huge.
Kenny pointed me to this fix.