issue 28: adding user verification per admin command (#28)

hi @whimboo !

here's a patch for issue 28. I've run some quick tests on it, seems ok.
this could perhaps still be tidied up some, but it is far better than the code it replaces in the first patch.
I've added some error-checking and tweaked the adminhelp array to support all this.
this library's whois check against a nick that's not logged in crashes the bot. 

it's safer to check only when the bot hears an admin command, since it checks the "from" nick, which had to be logged in to send the admin command