Major Description
PropertiesConfiguration has a property which controls whether include files are allowed. This property does not have a set method, it is set to true automatically if a base path is set. There may be scenarios in which it makes sense to support include files anyway, e.g. if they are specified as fully qualified file names or URIs or can be retrieved by the standard lookup mechanism.
So the set method should be public, and it makes sense to set this property to true per default. If a file contains an include property, the files it refers to should propably be loaded.
Also the get method for the property which controls file inclusion does not conform to the Java Beans specification; returning a boolean, it should start with the prefix is.