Use current version for install snippets

:fork_and_knife: If a specific cookbook version is selected use that version number for the install snippets and set the constraint to =.

![screen shot 2014-08-28 at 1 11 24 pm](https://cloud.githubusercontent.com/assets/316507/4079548/5cfa6c7e-2ed6-11e4-8f83-2cdc48d5bf11.png)

Closes #778.