Changes:
* Add validation to accept() to ensure file descriptors provided
refer to SOCK_STREAM sockets in the SOCK_LISTENING state
* Rather than writing a reply to the patty client socket when
accepting a SABM or SABME request, write a message to the
remote end of the listening socket; this avoids issues wherein
a client receives an unexpected accept() response that may be
unrelated to another pending request; this also allows client
code to use select(2) on listening sockets
* In patty_client_accept(), send the initial request to validate
that the local socket can accept connections, and then wait for
a connection to be made, reading a message written to the
listening socket from the patty server
* Allow select(2) to notify on accepted connections
Implement new patty client code, replacing src/call.c with src/client.c
providing clients with an interface dealing with file descriptors valid
in their process space; this also obviates the need to open a Unix
domain socket to a patty server explicitly, and helps keep track of
sockets opened on the server, locally
Changes:
* Implement patty_client_new() to handle opening the server Unix
domain socket, and to allocate a dict for mapping server-side
sockets with current process file descriptors
* Reimplement all server calls in src/call.c around the new
patty_client type; calls which result in the creation of a
Unix98 PTY by the patty server now handle opening the local PTY
and setting the file descriptor to raw mode. Furthermore, these
calls deal exclusively in terms of current process file
descriptors
* Refactor src/server.c to use the new patty_client type and calls
* Refactor examples/client.c, examples/server.c, examples/ax25dump.c
to use the new patty_client type and calls
* Fix a bug in src/server.c, respond_accept() wherein a 0, rather
than the file descriptor of the socket, is sent to the client as a
return value
