Content tokens should be generated from channel name

I don't know of a good way to demonstrate this with the current subset of modules, because I think only the watchdog module uses the content channels, but this started affecting me as I was impatiently refreshing my page with the ajax comments integration module :)

The problem:

When the page loads, if you call nodejs_send_content_channel_token() a random token is sent to the node server, and the same token is added in the JS so your auth requests will use that token value, they'll match up and all will be happy in the world.

However, if the node server is down when the token is sent there, the token won't make it into the tokenChannels[tokenChannel] list, but, your authData will be cached, causing its list of contentTokens to be used in every subsequent auth request.

So, if the node server is down and you connect, a random token is cached in authData.contentTokens and the tokenChannels list is empty. But now if you refresh, a new random token is inserted into tokenChannels[tokenChannel], but you'll still be using the old authData.contentTokens data which doesn't match and you'll never be able to connect to the channel.

The solution:

Make the token not random, and instead use the channel's name to generate.