Adds support for additional space on the bottom of the textarea.

Example of use case scenario:
![textarea](https://f.cloud.github.com/assets/766837/1612271/2bb52040-55c0-11e3-86b2-c25481319d18.png)

I've built a custom placeholder kindalike for my textareas. The extra space allows me to do so without overlapping the text. Could be useful for other stuff as well.