Feature request: Allow blacklist success detection for telnet instead of just whitelist

[rsheasby]

In case the title wasn't clear, here's my suggestion for success detection of telnet attempts:
Instead of looking for a specific message upon success, which may be hard or impossible to predict without having access already, it should rather infer success when the login error message is not returned, as most telnet servers will return a "Login incorrect" message on failed login. This can still be user-supplied.