[reSIProcate] BaseUsage.hxx: onReadyToSend generates an unused variable warning

[Alan Stokes <alan@xxxxxxxxxxxxxxxxx>]

BaseUsage.hxx recently acquired this line:
   virtual void onReadyToSend(SipMessage& msg) {}

However, that means when I build my code that uses this header (with
MSVC 7.1) I get an unused variable warning for msg. And since I compile
with warnings as errors, it breaks my build. 

This is the only place where this occurs in the headers. I think it's
common in the .cxx files, but that isn't an issue; I use resiprocate's
policy warning level when building resiprocate. But I'd like to be able
to use my policy when building my code.

Would it be possible to change it to:
  virtual void onReadyToSend(SipMessage&) {}

- Alan