Refactor Templates to expose platformExpander

This is needed to support the Windows build.
Clean up Utils.shakeToCabalVerbosity

Rather than use magic numbers which are needed when
issuing an external command to the cabal executable,
we can actually use Cabal's API value for verbosity,
then use fromEnum to convert back to an integer.
This change makes this function useable for mapping
Shake's verbosity to the Cabal API's verbosity.

hptool/src/Target.hs is modified to track this change.
Factor out localCommand into new file

The functions localCommand and localCommand'
(also helper function addPath') are moved from GhcDist
to a new file, hptool/src/LocalCommand.hs.  This
change allows these functions to now be used by the
OS-specific files, by preventing an import cycle.  The
other files included in this commit simply have their
imports modified (and note that most modules which
were importing GhcDist were doing so only for
localCommand.

* hptool/src/GhcDist.hs
* hptool/src/HaddockMaster.hs
* hptool/src/LocalCommand.hs
* hptool/src/Package.hs
* hptool/src/SourceTarballs.hs
* hptool/src/Target.hs
Correct spelling of "package.conf.d"

* hptool/src/Paths.hs
* hptool/src/Target.hs
Add LocalCommand to hptool.cabal

Forgotten file from "Factor out localCommand into new file"
Merge pull request #121 from randen/windows-1

Refactoring in preparation for Windows build