The `socket' function in the backends is only ever checked to see if

it's NULL. Since we already have one back end (uxpty) which doesn't
in fact talk to a network socket, and may well have more soon, I'm
replacing this TCP/IP-centric function with a nice neutral
`connected' function returning a boolean. Nothing else about its
semantics has currently changed.

[originally from svn r6810]

putty.h

@@ -357,7 +357,7 @@ struct backend_tag {
     void (*size) (void *handle, int width, int height);
     void (*special) (void *handle, Telnet_Special code);
     const struct telnet_special *(*get_specials) (void *handle);
-    Socket(*socket) (void *handle);
+    int (*connected) (void *handle);
     int (*exitcode) (void *handle);
     /* If back->sendok() returns FALSE, data sent to it from the frontend
      * may be lost. */