The getNameInfo API is a little strange

`getNameInfo` has the ability to report a name resolution error by means of returning `Nothing`. When the `NI_NAMEREQD` flag is not set, resolution will never fail because the function simply returns the IP address we were trying to look up. When `NI_NAMEREQD` is set, however, the function is supposed to fail when that address can't be resolved. Curiously enough, that failure is communicated through an `IOException` instead of simply returning `Nothing`! This is really surprising to me and I find myself writing code like

getNameInfo [NI_NAMEREQD] True False localAddr `catchIO` \_ -> return (Nothing,Nothing)

most of the time.

Is there any particular reason why an `IOException` is used to communicate a perfectly legitimate result of that function call?