- Add error messages when unimplemented functions are called on
  non-linux platforms.
- Implement retrieving the interface list on MacOS X (and other
  platforms that use NET_RT_DUMP).

Prevents paint_count values from being skewed when hiding windows.

rpcrt4: RPCRT4_strdupWtoA and RPCRT4_strdupAtoW don't change the input string, so make the input const.

rpcrt4: Stash away NetworkOptions passed in from the binding string so that transports can look at the string if needed.