- Linus Nielsen Feltzing reported and helped me repeat and fix a problem with

FTP with the multi interface: when a transfer fails, like when aborted by a
  write callback, the control connection was wrongly closed and thus not
  re-used properly.

  This change is also an attempt to cleanup the code somewhat in this area, as
  now the FTP code attempts to keep (better) track on pending responses
  necessary to get read in ftp_done().

lib/ftp.c

@@ -363,6 +363,7 @@ static void ftp_respinit(struct connectdata *conn)
   struct ftp_conn *ftpc = &conn->proto.ftpc;
   ftpc->nread_resp = 0;
   ftpc->linestart_resp = conn->data->state.buffer;
+  ftpc->pending_resp = TRUE;
 }
 
 /* macro to check for a three-digit ftp status code at the start of the
@@ -590,6 +591,8 @@ static CURLcode ftp_readresp(curl_socket_t sockfd,
   /* store the latest code for later retrieval */
   conn->data->info.httpcode=code;
 
+  ftpc->pending_resp = FALSE;
+
   return result;
 }
 
@@ -715,6 +718,8 @@ CURLcode Curl_GetFTPResponse(ssize_t *nreadp, /* return number of bytes read */
 
   } /* while there's buffer left and loop is requested */
 
+  ftpc->pending_resp = FALSE;
+
   return result;
 }
 
@@ -2305,6 +2310,8 @@ static CURLcode ftp_state_stor_resp(struct connectdata *conn,
                                SECONDARYSOCKET, ftp->bytecountp);
   state(conn, FTP_STOP);
 
+  conn->proto.ftpc.pending_resp = TRUE; /* we expect a server response more */
+
   return result;
 }
 
@@ -2417,6 +2424,7 @@ static CURLcode ftp_state_get_resp(struct connectdata *conn,
     if(result)
       return result;
 
+    conn->proto.ftpc.pending_resp = TRUE; /* we expect a server response more */
     state(conn, FTP_STOP);
   }
   else {
@@ -3161,6 +3169,7 @@ static CURLcode ftp_done(struct connectdata *conn, CURLcode status,
   case CURLE_REMOTE_ACCESS_DENIED:
   case CURLE_FILESIZE_EXCEEDED:
   case CURLE_REMOTE_FILE_NOT_FOUND:
+  case CURLE_WRITE_ERROR:
     /* the connection stays alive fine even though this happened */
     /* fall-through */
   case CURLE_OK: /* doesn't affect the control connection's status */
@@ -3239,7 +3248,8 @@ static CURLcode ftp_done(struct connectdata *conn, CURLcode status,
     conn->sock[SECONDARYSOCKET] = CURL_SOCKET_BAD;
   }
 
-  if((ftp->transfer == FTPTRANSFER_BODY) && !status && !premature) {
+  if((ftp->transfer == FTPTRANSFER_BODY) && ftpc->ctl_valid &&
+     ftpc->pending_resp && !premature) {
     /*
      * Let's see what the server says about the transfer we just performed,
      * but lower the timeout as sometimes this connection has died while the