Add a unuque identifier for installed packages (part 4 of 9)
Add a unuque identifier for installed packages (part 4 of 9)

Distribution.Simple.LocalBuildInfo: 

  - the LocalBuildInfo record contains an index of the installed
    packages; this has changed from PackageIndex InstalledPackageInfo
    to InstalledPackageIndex.

  - ComponentLocalBuildInfo stores the "external package dependencies"
    of the component, which was 
      componentPackageDeps :: [PackageId]
    and is now
      componentInstalledPackageDeps :: [InstalledPackageId]

  - we now export
      componentPackageDeps :: LocalBuildInfo -> [PackageId]
    (since to get the PackageId for an InstalledPackageId, you need
    to look it up in the InstalledPackageIndex, which is in the
    LocalBuildInfo)

  - similarly, previously
      externalPackageDeps :: LocalBuildInfo -> [PackageId]
    is now
      externalPackageDeps :: LocalBuildInfo -> [InstalledPackageId]


IreneKnapp/Faction,IreneKnapp/Faction