[Brutha]

So, who decides if they are 'authentic' documents - Wikileaks, surely?

Of course they aren't perfect and are human. Nobody is.
They however have shown in the past that they were willing to release documents that weren't in their own political interest.
The most damaging was an email list of all Wikileaks donors that someone uploaded to Wikileaks.
For the future the plan is to decentralize the system and provide the technology to allow other people to do the validating part. See the Knight Foundation Grand request: https://p10.secure.hostingprod.com/@...oundation.html
Wikileaks didn't got the grant and as a result it doesn't have the funds to work fast enough on new software but that doesn't mean that they aren't working on the problem of allowing different people to do the document authentication.

The recent release of the Iraq Warlogs and Cablegate contains additional retractions. At the start Wikileaks didn't want to retract anything to be more neutral. They conceded on that point to public pressure.
That again increases the need for decentralisation to get rid of the subjectivity problem.

There's work done inside Wikileaks to have software that allows others (probably people that the source chooses) to do the subjective judgement.

Among other things, because that didn't happen fast enough inside Wikileaks Daniel Domscheit-Berg (and as I understand a few anonymous others) left Wikileaks to work on the software solution outside Wikileaks.

So, which English dictionary definition would you go by?

Webster's definition is a good first step: "an expert at programming and solving problems with a computer"
Dictionary definitions however won't bring you very far when you talk about social movements. A dictionary isn't the place to look for an understanding about a ideological position or way of life that you don't yet understand.