Control spec is ambiguous whether a GETCONF error message is specified

The [spec for GETCONF response] says:

  If some of the listed keywords can't be found, Tor replies with a
  "552 unknown configuration keyword" message.

The spec also has a [about error messages]:

  Unless specified to have specific contents, the human-readable messages
  in error replies should not be relied upon to match those in this document.

Unfortunately, it's unclear what //specified to have specific contents// means here. The message for GETCONF is quoted, which at least in cursory read made me think it was //specified//. But I suppose it's ambiguous.

==== Expected change In discussion over IRC, arma suggested it...

might be even better to change the spec to be like "replies with a 552 message because of the unrecognized configuration key."

Overall, it was agreed upon amongst arma, meejah, sysrqb, and myself that the spec shouldn't be denoting a specific message here, and that controllers shouldn't rely on a specific message. Only the numeric code 552 should be relied upon.