Fix a ton of incorrect behaviour regarding numerics.

- Change m_abbreviation to use ERR_UNKNOWNCOMMAND instead of 420.
- Change m_autoop to use ERR_UNKNOWNMODE instead of 415 which
  conflicted with ERR_BADMASK from RFC 2812.
- Change m_cban to use ERR_NOSUCHCHANNEL instead of 384 which
  conflicted with RPL_MYPORTIS from RFC 1459.

- Fix m_ssl_gnutls using numbers instead of constants.