patch applied (cabal): Fix error message regression

[Simon Marlow]

Wed Jun  6 07:26:50 PDT 2007  Simon Marlow <simonmar at microsoft.com>
  * Fix error message regression
  
  Passing a non-existent program for --with-hc-pkg used to say this:
  
  $ ./Setup configure --with-hc-pkg=foo
  Configuring QuickCheck-2.0...
  /bin/sh: foo: command not found
  Setup: executing external program failed: "foo" --global list >tmp23634
  
  Now it is rather less useful:
  
  $ ./setup configure --with-hc-pkg=foo
  configure: Reading installed packages...
  zsh: 23596 exit 127   ./setup configure --with-hc-pkg=foo
  
  This patch restores the old behaviour, slightly improved:
  
  $ ./Setup --with-hc-pkg=foo configure
  configure: Reading installed packages...
  Setup: executing external program failed (exit 127) : foo --global list

    M ./Distribution/Simple/Utils.hs -2 +7