CountVectorizer Rewrite

Rewrote CountVectorizer fit transform.  I did some tests and it performs about 40% faster.  For example, here's the plot on my dataset of 50000 English documents of 150-1000 words in length.  It passes all the tests in the sklearn/feature_extraction/tests/test_text.py
![countvect_1](https://f.cloud.github.com/assets/786402/259497/40bfd536-8cbf-11e2-89c6-99099cd87f50.png)