Pass --reorder-goals to "cabal install"...

Tweaks the cabal dependency resolution heuristics in some undocumented
way that makes cabal more likely to solve Yesod dependencies.  (Without
this you see odd errors like yesod-platform getting rejected because it
depends on a conflicting version of, say, aeson, than your app does,
even though your .cabal file doesn't actually specify which version of
aeson, and the whole point of yesod-platform was to lock it to a version
that would work.)

This feels like black magic, but it's recommended by the Yesod
documentation: http://www.yesodweb.com/page/quickstart :(
Merge pull request #24 from samstokes/cabal-reorder-goals

Pass --reorder-goals to "cabal install"
Allow customization through env vars
Merge pull request #25 from begriffs/env_dir

Allow customization through env vars
Merge branch 'master' of github.com:begriffs/heroku-buildpack-ghc into prebuilt-library

Conflicts:
	bin/compile