Fixes TypeError when installing without freetype

When `freetype-config` is missing, setup.py crashes with TypeError. This fixes it and allows the "required packages" info to be printed.

Log of the error installing 1.4.0:

```
(venv-mpl)remram@vebian:~$ pip install -U matplotlib
Downloading/unpacking matplotlib
  Downloading matplotlib-1.4.0.tar.gz (51.2MB): 51.2MB downloaded
  Running setup.py (path:/tmp/venv-mpl/build/matplotlib/setup.py) egg_info for package matplotlib
    ============================================================================
    Edit setup.cfg to change the build options

    BUILDING MATPLOTLIB
                matplotlib: yes [1.4.0]
                    python: yes [2.7.8 (default, Aug 10 2014, 16:19:34)  [GCC
                            4.9.1]]
                  platform: yes [linux2]

    REQUIRED DEPENDENCIES AND EXTENSIONS
                     numpy: yes [not found. pip may install it below.]
                       six: yes [six was not found.]
                  dateutil: yes [dateutil was not found. It is required for date
                            axis support. pip/easy_install may attempt to
                            install it after matplotlib.]
                   tornado: yes [tornado was not found. It is required for the
                            WebAgg backend. pip/easy_install may attempt to
                            install it after matplotlib.]
                 pyparsing: yes [pyparsing was not found. It is required for
                            mathtext support. pip/easy_install may attempt to
                            install it after matplotlib.]
                     pycxx: yes [Couldn't import.  Using local copy.]
                    libagg: yes [pkg-config information for 'libagg' could not
                            be found. Using local copy.]
    Traceback (most recent call last):
      File "<string>", line 17, in <module>
      File "/tmp/venv-mpl/build/matplotlib/setup.py", line 154, in <module>
        result = package.check()
      File "setupext.py", line 940, in check
        if 'No such file or directory\ngrep:' in version:
    TypeError: argument of type 'NoneType' is not iterable
    Complete output from command python setup.py egg_info:
    ============================================================================

Edit setup.cfg to change the build options



BUILDING MATPLOTLIB

            matplotlib: yes [1.4.0]

                python: yes [2.7.8 (default, Aug 10 2014, 16:19:34)  [GCC

                        4.9.1]]

              platform: yes [linux2]



REQUIRED DEPENDENCIES AND EXTENSIONS

                 numpy: yes [not found. pip may install it below.]

                   six: yes [six was not found.]

              dateutil: yes [dateutil was not found. It is required for date

                        axis support. pip/easy_install may attempt to

                        install it after matplotlib.]

               tornado: yes [tornado was not found. It is required for the

                        WebAgg backend. pip/easy_install may attempt to

                        install it after matplotlib.]

             pyparsing: yes [pyparsing was not found. It is required for

                        mathtext support. pip/easy_install may attempt to

                        install it after matplotlib.]

                 pycxx: yes [Couldn't import.  Using local copy.]

                libagg: yes [pkg-config information for 'libagg' could not

                        be found. Using local copy.]

Traceback (most recent call last):

  File "<string>", line 17, in <module>

  File "/tmp/venv-mpl/build/matplotlib/setup.py", line 154, in <module>

    result = package.check()

  File "setupext.py", line 940, in check

    if 'No such file or directory\ngrep:' in version:

TypeError: argument of type 'NoneType' is not iterable

----------------------------------------
Cleaning up...
```
It is not obvious to me that what ever makes the call fail should be handled the same as the case this if statement is supposed to catch (where the call succeeds (returns 0), but does not work).