modification on preprocess

Modified `preprocess` so it can handle this case:

    cellbox = 
      RowBox[{RowBox[{"gcd", "[", RowBox[{"m0_", ",", "n0_"}], "]"}], 
        ":=", "\[IndentingNewLine]", 
        RowBox[{"Module", "[", 
          RowBox[{RowBox[{"{", 
              RowBox[{RowBox[{"m", "=", "m0"}], ",", 
                RowBox[{"n", "=", "n0"}]}], "}"}], ",", 
            "\[IndentingNewLine]", 
            RowBox[{RowBox[{"While", "[", 
                RowBox[{RowBox[{"n", "\[NotEqual]", "0"}], ",", 
                  RowBox[{RowBox[{"{", RowBox[{"m", ",", "n"}], "}"}], 
                    "=", "     ", 
                    RowBox[{"{", 
                      RowBox[{"n", ",", 
                        RowBox[{"Mod", "[", 
                        RowBox[{"m", ",", "      ", "n"}], "]"}]}], 
                      "}"}]}]}], "]"}], ";", "\[IndentingNewLine]", 
              RowBox[{RowBox[{"m", " ", "n"}], "+", 
                RowBox[{"2", " ", "3"}], "+", 
                RowBox[{"4", "     ", "5"}]}]}]}], "\[IndentingNewLine]", 
          "]"}]}];
    FullCodeFormat[cellbox] // CellPrint[Cell[BoxData[#], "Input"]] &

![image](https://cloud.githubusercontent.com/assets/2263328/3949658/0c6ded9a-26ba-11e4-8051-753d20b4ceae.png)