Error with installing latest developer version of matplotlib on Travis

I am using Travis to test another package (http://github.com/aplpy/aplpy) that depends on Matplotlib, and when executing this line:

```
- pip install git+http://github.com/matplotlib/matplotlib.git#egg=matplotlib
```

I get the error:

```
$ pip install git+http://github.com/matplotlib/matplotlib.git#egg=matplotlib
Downloading/unpacking matplotlib from git+http://github.com/matplotlib/matplotlib.git#egg=matplotlib
  Cloning http://github.com/matplotlib/matplotlib.git to /home/travis/virtualenv/python2.6/build/matplotlib
  Running setup.py egg_info for package matplotlib
    The required version of distribute (>=0.6.45) is not available,
    and can't be installed while this script is running. Please
    install a more recent version first, using
    'easy_install -U distribute'.
    
    (Currently using distribute 0.6.34 (/home/travis/virtualenv/python2.6/lib/python2.6/site-packages/distribute-0.6.34-py2.6.egg))
    Complete output from command python setup.py egg_info:
    The required version of distribute (>=0.6.45) is not available,
and can't be installed while this script is running. Please
install a more recent version first, using
'easy_install -U distribute'.
(Currently using distribute 0.6.34 (/home/travis/virtualenv/python2.6/lib/python2.6/site-packages/distribute-0.6.34-py2.6.egg))
```

@mdboom - I think this is why the header of ``setup.py`` in Astropy is more complex: https://github.com/astropy/astropy/blob/master/setup.py