Add the __doc__ string from the original module on copy_none().

Lib/rexec.py

@@ -244,7 +244,9 @@ def copy_only(self, src, names):
         return dst
 
     def copy_none(self, src):
-        return self.add_module(src.__name__)
+        m = self.add_module(src.__name__)
+        m.__doc__ = src.__doc__
+        return m
 
     # Add a module -- return an existing module or create one