Add a new back-end function to return the exit code of the remote

process. This is functional in SSH, and vestigial (just returns 0)
in the other three protocols. Plink's Windows exit code is now
determined by the remote process exit code, which should make it
more usable in scripting applications. Tested in both SSH1 and SSH2.

[originally from svn r1518]

raw.c

@@ -162,6 +162,12 @@ static int raw_ldisc(int option)
     return 0;
 }
 
+static int raw_exitcode(void)
+{
+    /* Exit codes are a meaningless concept in the Raw protocol */
+    return 0;
+}
+
 Backend raw_backend = {
     raw_init,
     raw_send,
@@ -169,6 +175,7 @@ Backend raw_backend = {
     raw_size,
     raw_special,
     raw_socket,
+    raw_exitcode,
     raw_sendok,
     raw_ldisc,
     raw_unthrottle,