remove any pending selects when closing the socket.

mdetach.c

@@ -17,6 +17,10 @@ int mdetach(Entry *e, void *p1, void *p2, void *p3, void *p4, void *p5)
     IncBusy();
     TCPIPCloseTCP(e->ipid);
     
+    // hmmm this is in the close() call, so the 
+    // fd won't be valid afterwards....
+    e->select_rd_pid = 0xffff;
+    e->select_wr_pid = 0xffff;
     e->command = kCommandDisconnectAndLogout;
     e->cookie = 0;
     e->timeout = timeout;