Fail to build if the app/lib directory is empty

[DavidWhitlock]

A student and I discovered that a very confusing java.lang.ClassFormatError: Truncated class file error is issued when the jar files in the app/lib directory do not exist.

On one machine (a PSU Linux machine), this student had created the koans project using the Maven archetype. The archetype created the app/lib directory and its four jar files. When the student pulled those changes into a checkout on a different machine (a Windows machine), the koan source code did not compile and a Truncated class file exception was thrown for the Koan class.

I need to bullet-proof the Maven project to provide a more intelligible message when the app/lib directory does not contain jar files.