The session needs to be rolled back after an error before we're able to
start a new transaction.

This should make it easier to do scans more often and with less delay
after a file has been uploaded. Activated with the -p/--poll argument.
Without this argument the scanner runs in the default one-shot mode.

This will cause the file handler to return 404 instead of 500.

This is needed for the proper request URLs to be detected during login.

Add some local .cfg files, but exclude setup.cfg

We do this in the filesystem storage module instead.