get_prerequisites empties the prerequisite list when target does not exist
In the beginning of the function get_prerequisites in the GetPrerequisites module, there is a small block of code that empties the prerequisites list if the target passed into the function doesn't exist. This caused a problem for me because some of the libraries I was installing and subsequently calling get_prerequisites (recursively) on depended on some other libraries in my project that hadn't made it into the install folder yet. The fact that they were missing at the time didn't matter, so I ignored the warning and was confused when my install folder was missing some dependencies. I can see why you would print a message and exit the function, but is there a need to empty the list?