WinHugs, add /edit flag

Hi, This patch adds an /edit flag. The behaviour of winhugs on: winhugs.exe /edit filename.hs is to fire up whichever editor is configured with winhugs and exit winhugs. The massive advantage of this is a user can set winhugs /edit as their file handler for editing haskell files, and as they change the option in winhugs, it gets changed in their system. This patch lays the groundwork for a new installer (expect that patch tomorrow :) ) Neil