#497 Enable excluding paths from source directories

[Jeremy Whitlock]

In the Java support for Eclipse, you can specify a directory containing class files. You can further tell Eclipse to exclude descendants. Pydev could benefit from this feature as well as I have a Django project that uses a data directory within the project that can end up with Python sources within it and those paths get indexed and cause entries in the Problems viewer even though those sources are really a part of my project.