Ubuntu: ghc man page not accessible

On my system (Ubuntu 14.04), the following directories did not exist yet:
* /usr/local/share/doc
* /usr/local/share/man/man1

Therefore, the activate script created the following erronous links:
* /usr/local/share/doc -> /usr/local/haskell/ghc-7.8.3-x86_64/share/doc/ghc/
* /usr/local/share/man/man1 -> /usr/local/haskell/ghc-7.8.3-x86_64/share/man/man1/ghc.1

Here is a fix.