return resumeable upload collision error during session creation
When uploading with the resumeable upload API (upload.createSession) with @name.conflictBehavior : fail, it currently only returns a "nameAlreadyExists" error once the upload is completed.
It would be much nicer to have an error returned on the initial createSession call already. This saves apps either an extra api call before the upload to check if a file already exists, or saves a lot of bandwitdh if it's just uploaded without checking first.
The same would also be useful for max filesize exceeded errors, although that's much easier to check clientside so not that useful.