[Xmonad] a safer ghci prompt

Hi, attached you'll find a safer ghci prompt, that uses an external program to evaluate haskell expression. This is still work in progress, but you can have an idea of what I'd like to do. Feedback highly appreciated! ciao andrea ps: to use: 1. save the attached file as GhcPrompt.hs and follow the install instruction; 2. save and compile the uitlity you'll find at the end of the file. 3. enjoy.