Added Connection::GetURI()

This function returns a URI of the resource that the connection is connected to. This is especially important for connections established by accepting a connection from a remote host.

Also added implementations for ConnectionMachPort, ConnectionSharedMemory, 
Also fixed up some documentation in Connection::Write
Renamed ConnectionFileDescriptorPosix::SocketListen to ConnectionFileDescriptorPosix::SocketListenAndAccept
Fixed a log message in Socket.cpp

Differential Review: http://reviews.llvm.org/D7026

llvm-svn: 226362