python2.4 compatibility

Get all tests passing with python 2.4:
+ add Jason's pure python defaultdict
+ fix usage in testkmlparser.py, similar to r1212

Tested by running
nosetests-2.4
which I installed with
sudo easy_install-2.4 nose

[Tom, 2009-11-30 22:56:57]

I'd like to keep the tools running in python2.4 because it is the only version
guaranteed to be on every machine at Google. I'm also going to update
http://code.google.com/p/googletransitdatafeed/wiki/CodeReview with a reminder
to test for 2.4 compatibility.

[Tom, 2009-12-01 19:14:14]

I updated this with raw email removed and using same indentation as the rest of
util.py. Please take a look.

[anog, 2009-12-02 21:56:41]

Looks good to me.

[Tom, 2009-12-03 15:31:21]

On 2009/12/02 21:56:41, anog wrote:
> Looks good to me.

Submitted as r1227