Adds a Sized Button Test

This demonstrates the button sizing discrepancy reported in issue #271. Anchor buttons with explicit widths (`pure-input-1*`) contained in forms are too wide and break out of containing boxes. This seems to be a result of left and right padding being applied on top of the defined width.

The anchor button is too wide:

![screen shot 2014-01-12 at 10 45 07 am](https://f.cloud.github.com/assets/8320/1896462/4a5ee4ac-7ba1-11e3-827c-c7ae9a63af2c.png)

I'm putting this in a separate pull request from my proposed solution.