(this is number 3 of 9 commits to be applied together)

  Following Haskell 98, if the module declaration is omitted it now
  defaults to "module Main(main) where", rather than the previous
  default of exporting everything.

  Furthermore, "module Main where" also defaults to exporting just
  Main.main rather than everything in the module (modules other than
  Main behave as normal).  This permits the usage inference to give
  better results for the Main module, since exported functions get
  worse types than nonexported functions.