Added --bt-lpd-interface option to specify the interface to use
for Local Peer Discovery. LpdMessageDispatcher object now has its
own socket. LpdMessageReceiver's socket is binded to multicast
address to only receive multicast packets.
* src/BtSetup.cc
* src/LpdMessageDispatcher.cc
* src/LpdMessageDispatcher.h
* src/LpdMessageReceiver.cc
* src/LpdMessageReceiver.h
* src/LpdReceiveMessageCommand.cc
* src/LpdReceiveMessageCommand.h
* src/OptionHandlerFactory.cc
* src/SocketCore.cc
* src/SocketCore.h
* src/prefs.cc
* src/prefs.h
* src/usage_text.h
* test/LpdMessageDispatcherTest.cc
* test/LpdMessageReceiverTest.cc