Inherit the width of pre code inside the input code cells.

This fix a ugly bug because of different widths between pre code inside de cells and the cell itself.
Pics attached... see the right border of the cell... 
**Before the fix:**

![fix_pre_1](https://f.cloud.github.com/assets/1640669/1608718/95f9fe12-5511-11e3-8cbd-563e45f64ea8.png)

**And after the fix:**

![fix_pre_2](https://f.cloud.github.com/assets/1640669/1608719/a116e1e8-5511-11e3-997c-2120613fafef.png)