Correctly close server connection when client disconnects.

When the server disconnected, we were forwarding that information to the
client.  But we weren't forwarding back the other way when the client
disconnected since there was no callback in place to do that.

Relatedly, when we failed entirely to connect to the server, we didn't notify the
client right away.  Now we do.

Thanks to 'Roger' on the mailing list for pointing out these bugs.

ssnet.py

@@ -15,7 +15,7 @@ CMD_EXIT = 0x4200
 CMD_PING = 0x4201
 CMD_PONG = 0x4202
 CMD_CONNECT = 0x4203
-# CMD_CLOSE = 0x4204   # never used - removed
+CMD_STOP_SENDING = 0x4204
 CMD_EOF = 0x4205
 CMD_DATA = 0x4206
 CMD_ROUTES = 0x4207
@@ -27,6 +27,7 @@ cmd_to_name = {
     CMD_PING: 'PING',
     CMD_PONG: 'PONG',
     CMD_CONNECT: 'CONNECT',
+    CMD_STOP_SENDING: 'STOP_SENDING',
     CMD_EOF: 'EOF',
     CMD_DATA: 'DATA',
     CMD_ROUTES: 'ROUTES',
@@ -106,6 +107,8 @@ class SockWrapper:
     def seterr(self, e):
         if not self.exc:
             self.exc = e
+        self.nowrite()
+        self.noread()
 
     def try_connect(self):
         if self.connect_to and self.shut_write:
@@ -162,8 +165,6 @@ class SockWrapper:
         except OSError, e:
             # unexpected error... stream is dead
             self.seterr(e)
-            self.nowrite()
-            self.noread()
             return 0
         
     def write(self, buf):
@@ -231,6 +232,11 @@ class Proxy(Handler):
         self.wrap2 = wrap2
 
     def pre_select(self, r, w, x):
+        if self.wrap1.shut_read: self.wrap2.nowrite()
+        if self.wrap1.shut_write: self.wrap2.noread()
+        if self.wrap2.shut_read: self.wrap1.nowrite()
+        if self.wrap2.shut_write: self.wrap1.noread()
+        
         if self.wrap1.connect_to:
             _add(w, self.wrap1.rsock)
         elif self.wrap1.buf:
@@ -430,6 +436,7 @@ class MuxWrapper(SockWrapper):
     def noread(self):
         if not self.shut_read:
             self.shut_read = True
+            self.mux.send(self.channel, CMD_STOP_SENDING, '')
             self.maybe_close()
 
     def nowrite(self):
@@ -464,6 +471,8 @@ class MuxWrapper(SockWrapper):
     def got_packet(self, cmd, data):
         if cmd == CMD_EOF:
             self.noread()
+        elif cmd == CMD_STOP_SENDING:
+            self.nowrite()
         elif cmd == CMD_DATA:
             self.buf.append(data)
         else: