static method that calls os.walk, but filters out
		anything that doesn't match the filter

def _filtered_walk(path, file_filter):
		"""
		static method that calls os.walk, but filters out
		anything that doesn't match the filter
		"""
		for root, dirs, files in os.walk(path):
			log.debug('looking in %s', root)
			log.debug('files is %s', files)
			file_filter.set_root(root)
			files = filter(file_filter, files)
			log.debug('filtered files is %s', files)
			yield (root, dirs, files)