Update a reg entry for WinGHCi
Update a reg entry for WinGHCi

* hptool/os-extras/win/templates/Nsisfile.nsi.mu
  * winGHCi adds some reg entries when it is run, and one
    "WorkdingDir", it reads but never updates if it already
    exists, causing winGHCi associated with any newer HP
    installs to use an old value. So, create and remove this
    particular entry when we do the install.

ardumont/haskell-platform,erantapaa/haskell-platform,erantapaa/haskell-platform,ardumont/haskell-platform,gbaz/haskell-platform,erantapaa/haskell-platform,gbaz/haskell-platform