* added retroshare/rsdht.h
* extended p3bitdht to provide RsDht interface. (p3bitdht_interface.cc)
* added UdpRelay to networking stack.
* started expansion of p3bitdht to handle connections.
* added <string> header to rsthreads.
git-svn-id: http://svn.code.sf.net/p/retroshare/code/trunk@4399 b45a01b8-16f6-495d-af2f-9b41ad6348cc