patch applied (ghc): :unset settings support

[Simon Marlow]

Tue Nov 23 11:01:32 PST 2010  Boris Lykah <lykahb at gmail.com>
  * :unset settings support
  Added support for settings [args, prog, prompt, editor and stop].
  Now :unset supports the same set of options as :set.

    M ./ghc/InteractiveUI.hs -17 +32

View patch online:
http://darcs.haskell.org/cgi-bin/darcsweb.cgi?r=ghc;a=darcs_commitdiff;h=20101123190132-ba5be-05232bcb3fb9a5faa833b26f1c29e1695cea838f.gz