Hardening/619 forbidden characters

### Description
o The response to 'Service not found: $URL' changed to 'unrecognized request', to avoid to respond with the data that the user supplied (security risk)
o Requests with any of the 'forbidden characters' in the values of the payload (see issue #619) are refused, both for XML and JSON.

Yes, it is a bug discovered during this PR/branch.
And sure, a line in CHANGES_NEXT_RELEASE is in order.