Expand tilde-paths for calling hoogle locally

The current document suggests adding path elements like "~/.cabal/bin"
(a.k.a. "tilde-paths") to the PATH environment variable and the
`exec-path' variable.  I had some trouble with this when using zsh as my
default shell -- in particular, efforts to call hoogle locally would
error out with the message: "zsh:1: command not found: hoogle".  There
were no such problems when I used bash as my default shell.

A resonably robust solution to this problem is to wrap tilde-path
elements like this in a call to `expand-file-name', which will expand
them to absolute paths - a situation which I'd expect every shell to
handle properly.  (I've tested with both bash and zsh and they, at
least, have no problem with this.)
Merge branch 'master' of https://github.com/dpkatz/emacs-haskell-tutorial