Wiki history (#12): show links to diffs
Added a "proxy" handler for ugly wiki diff URLs.

Rewrites /w/foobar/diff?start=23&end=42 to /w/foobar/diff/23/42. We're
going to need this for form-based diff revision selection.
Show radio buttons in wiki history instead of links

Select diff revisions wikipedia-style, with two columns of radios.
Merge branch 'master' of github.com:dlthomas/snowdrift into dlthomas