Keep run_str on orig_run_str to help subclasses

waflib/Task.py

@@ -86,6 +86,8 @@ class store_task_type(type):
 				# if a string is provided, convert it to a method
 				(f, dvars) = compile_fun(cls.run_str, cls.shell)
 				cls.hcode = cls.run_str
+				cls.orig_run_str = cls.run_str
+				# change the name of run_str or it is impossible to subclass with a function
 				cls.run_str = None
 				cls.run = f
 				cls.vars = list(set(cls.vars + dvars))