slack should warn when you are about to apply a role that is not in the host's configuration

[GoogleCodeExporter]

What steps will reproduce the problem?
1. pass a role to slack on the command line that would not be slacked by
running slack without arguments
2.
3.

What is the expected output? What do you see instead?
slack should warn you the role your slacking is not currently part of the
host's configuration and either prompt you to continue or required you to
re-run the command using --force or similar option

What version of the product are you using? On what operating system?
0.15.2.tar.gz

Please provide any additional information below.
It should not be so easy to mess up your systems by slacking the wrong roles.

Original issue reported on code.google.com by [email protected] on 2 Apr 2009 at 4:22