The redirect.PrefixHandler redirects "/foo/" to "/foo", which is what
we want in most cases ("/cl/", "/change/", etc) but not here.
So wrap it with a handler that handles "/blog/" explictly.
R=dsymonds
CC=golang-dev
https://golang.org/cl/14326043
Defer parsing of blog content until accessed for faster startup.
Fall back on redirect if blog content unavailable locally.
R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/13335052