Don't allow stray \r or \n in command parameters

Don't allow stray \r or \n in command parameters

If ngircd receives an input line like "COMMAND arg\nIRRELEVANT\r\n",
"arg\nIRRELEVANT" is passed as an argument to COMMAND. This can lead
to output like:

:ngircd.test.server 322 nick #chan 1 :
topicwithprecedingnewline
:ngircd.test.server 322 nick #nxtchan 1 :
[..]

Worse, this allows clients to piggyback irc commands, e.g.
"TOPIC #a :test\n:fake!~a@nonexistant JOIN :#a\r\n", which
causes the client to receive a JOIN command during /LIST output.

Bug reported by Scott Perry, first patch by Florian Westphal.