Download page and D docs defaulting to D2

[Brian Hay]

Christopher Wright wrote:
> These issues are fixed. Yay! The obvious links that I can find are, anyway.

Not quite. Everything in the left sidebar still links to D2 by default. 
There should also be some notice on the new home page that D1 is stable 
whereas D2 is not. At the moment they aren't differentiated and people 
will naturally select the D2 link assuming it is better and safe to use.