Removed dependency on RTPproxy from rtpproxy.org. The reasons for this are:

Removed dependency on RTPproxy from rtpproxy.org.  The reasons for this are:
 * RTPproxy is more complex than needed for simple 6/4 translation
 * RTPproxy is hardly documentated, making it an unreliable basis for SIPproxy64
 * RTPproxy is intended for very large setups; our scaling to 12500 conversations is enough?

There is a lot of work left to be done, most notably cleanup of the code now that it
works and closing sockets.  But that can be done as part of a major restructuring
operation in the master branch.