First stab at an installer package for the Mac

First stab at an installer package for the Mac
- GHC as a Mac framework
- I tried to make a package where the user could choose whether to install
  in /Library/Frameworks or ~/Library/Frameworks (to allow installation for
  non-admins).  However, that doesn't work well without including the whole
  distribution twice as the decision as to whether the admin password needs
  to be entered is made at packaging time (not at install time).