Rename make_pipe.hh to socketpair.hh
Move make_pipe to static member function of UnixDomainSocket
Rename make_pipe() -> make_pair()
Make PacketShell store a (non-stripped) UnixDomainSocket
file_descriptor.hh: g++ < 4.9 requires a virtual destructor to inherit
Make Socket/SecureSocket/TunDevice inherit from FileDescriptor
Make UnixDomainSocket have private constructor
socketpair.cc: Implement send_fd/recv_fd
packetshell.cc: Write directly to sibling's TUN device (big CPU win)