Adds error messaging to Parser when a class cannot be found.

When attempting to implement paratest into our code base, I was presented with the following:

![screen shot 2014-12-30 at 9 25 38 am](https://cloud.githubusercontent.com/assets/1444395/5580863/dd1ab978-9005-11e4-831a-c72e6acfc16b.png)

This pull request adds more specific messaging when a class does not exist in the provided srcPath.