Update structured-haskell-mode.rcp

- structured-haskell-mode provides the feature "shm" (presumably because
  "structured-haskell-mode" is too long a name)

- Running `cabal configure` right before `cabal install` is fruitless
  and can actually fail even when `cabal install` would succeed.  See
  http://ircbrowse.net/day/haskell/2014/06/02?id=18252351&timestamp=1401731943#t1401731943 .