SWC-1771: do a precheck
Merge pull request #1239 from jay-hodgson/SWC-1771

SWC-1771: do a precheck
Merge branch 'develop' of ssh://github.com/Sage-Bionetworks/SynapseWebClient into SWC-1663
keep track of upload type being used, and handle servlet response
update to real sftp proxy (thanks to Xa)