[reSIProcate] added an Aor class

[Jason Fischl]

I put together an interface and implementation for an Aor class in 
resiprocate. Currently, there is a call Uri::getAor() that returns a 
Data. This would change to return a const Aor& instead. It will be 
possible to make Uri from an Aor and vice-versa. Comparison rules for 
Aor are much simpler than for Uri.

A major difference is that in Aor, the scheme is included whereas with 
the current Data version it is not.

This will have an impact on existing applications using resiprocate so I 
am not suggesting that we adopt this right away. Please provide comments 
on the proposed changes and we'll consider making the change after the 
next release. I have not integrated Aor into Uri yet so there are no 
impacts on your code for now.

An interim solution would be to provide a new interface on Uri which 
returns the Aor and leave the existing interface for Data::getAor().

Proposed interface additions to Uri:

Uri::Uri(const Data& aor);
const Aor& Uri::aor() const;


Jason