Make linkify even faster

This makes it a few orders of magnitude faster still:

Before:
![screen shot 2014-06-25 at 14 05 19](https://cloud.githubusercontent.com/assets/286476/3385373/6a61ea8a-fc69-11e3-908a-15a7cba1d767.png)

After:
![screen shot 2014-06-25 at 14 05 24](https://cloud.githubusercontent.com/assets/286476/3385375/6f2ffc5a-fc69-11e3-9ee5-3247871cab07.png)


I don't understand. What is difficult?