Ajax parameters option should not be a raw string

See http://www.prototypejs.org/api/ajax/options
  This can be provided either as a URL-encoded string or as any
  Hash-compatible object (basically anything), with properties representing
  parameters.

Prototype 1.5.1.1 encodes parameters, but 1.7.0 does not.
If Jenkins uses 1.7.0, he warns us of container's encoding
regardless of container's configuration.