These are now checked at client side (not CDN side), so not actually an error worth collecting.
Also removed "Uploading the same file from multiple tabs or windows is not allowed." -- no longer exists.
`doError` supported either a string or object, and so far there are no instances where the object version is used, so this enhancement should be safe to do without affecting anyone.
## Change
For the object version, support an additional `cause` parameter that will be logged but not show in the GUI.
