#15 Scrubbing output folder before saving transformed code

[Thomas Genssler]

The output folder should be emptied before the
transformation result is written back to disk.
Otherwise, remainings of earlier transformations may
still exist and may thus cause confusion. Example:
Adding "delete class" to a script - if the script has
been ran before, the deleted class may still exist in
the output folder. Although it is deleted from the
Inject/J model instances, the compilation unit (i.e.,
the *.java file) is not deleted in the output folder.