excluding "generated" dirs when building targets.mk

mktargets.py

@@ -53,6 +53,9 @@ class TargetMaker(object):
     def _add_deps_from_alt_source_file_extensions(self, as_swf, rel_mxml):
         basedir = dirname(rel_mxml)
         for dirpath, dirnames, filenames in os.walk(basedir):
+            for i, directory in enumerate(dirnames):
+                if directory == 'generated':
+                    dirnames.pop(i)
             for filename in filenames:
                 if ext(filename) in self._source_fileexts:
                     rel_source = relpath(pathjoin(dirpath, filename), HERE)