Check validity of turk module; update if needed

[jodeleeuw]

I believe that the automatic worker ID detection no longer works with the most common ways of setting up experiments on MTurk. This needs to be verified, and then solved (if possible).

[jodeleeuw]

The issue appears to be caused by Amazon's switch to HTTPS. The document.referrer is empty if the current page is served via HTTP and the previous via HTTPS. Need to verify, and then modify documentation to be clear about the limitations.

[jodeleeuw]

I wonder if this should be removed for 8.0 and made into a separate package? It seems like code to interface with 3rd party tools should be standalone packages.