Only log "IDENT ... no result" when IDENT was looked up

Without this patch, ngIRCd logged the "IDENT lookup for connection X:
no result"-message even when IDENT lookups have been disabled using the
"Ident = no" configuration option, which is a little bit misleading.

Reported by "btwe" in #ngircd.
Revamp parameter checks

Move most of the parameter checks into Handle_Request().
Add missing penalty times before returning numeric 461.
Ensure parameters are checked before anything else (i.e. checking for op
privileges or Conf_MorePrivacy).
Correct numeric returned by whois if no nick is supplied (as per RFC).
Minor cosmetic changes

Add a define to indicate any client.  While I'm here use hex values instead
of decimal, it's somewhat clearer that they could be OR'ed together.