pkstream/pkstream.c: Allow multiple listening and peer addresses.

When being a TCP server.

  * Accept multiple `-b' and `-p' options, and accumulate their values
    into string vectors;

  * expand the `connwait' addresses into vectors;

  * when resolving addresses, accumulate the addresses into the
    appropriate result vectors;

  * maintain multiple `sel_file' objects waiting for their respective
    listening sockets;

  * and search the vector of peers when accepting incoming
    connections (an empty vector means that all remote addresses are
    permitted, so we no longer need to dig into the address structure
    here).