fix bug in command-not-found handling (using fail instead of exit code).
fix bug in command-not-found handling (using fail instead of exit code).

Ignore-this: 38032f7da8a9b9f94bc01f3af746428f

darcs-hash:20081207212153-72aca-9b2a573422814b32863a4564d07e6fbe2ca86540

shicks/shsh,shicks/shsh