[devtools] fix race when creating backupdir If somebody else creates backupdir between our stat() and mkdir() (like, say, another test running in parallel), we shouldn't crash.

[staticcontrollers] Raise Forbidden, not Unauthorized Unauthorized means "log in to get access", as it results in a HTTP 401. Here, the error is pretty much permanent, and returning 401 instead of 403 confuses things terribly. (This seems to be a pretty widespread confusion :/)