Support multiple module's in one file

[Neil Mitchell]

The Haskell standard says nothing about the relationship between modules and files, so the following program is legitimate:

module A where
a :: Int
module B where
b :: Int

Hoogle uses files such as this to store the information generated by Haddock. Hoogle will be switching to use haskell-src-exts shortly, but with a preprocessing hack to split up the module declarations. If HSE supported multiple modules within one file it would be easier.

[nibro]

This has actually worked for some time now, seems I've forgotten to close the ticket.