This allows godoc.org to work on nested packages. As it stood gddo would
fail trying to find nested packages. Let's say we have a vaind with this
route:
go.mcquay.me/vain -> https://s.mcquay.me/sm/vain
Asking godoc for go.mcquay.me/vain would work fine. However trying to
get documentation for go.mcquay.me/vain/errors (nested package) would
return 404 since it wouldn't match known paths exactly.
Since now we match and return "go.mcquay.me/vain" for the full path,
gddo is able to use local caches for its information.
Change-Id: I599a75898493734fc652e507f477c11b1b1b13e8
