Add comment to automatically generated scripts.

setupbase.py

@@ -334,6 +334,7 b' def find_entry_points():'
     return [e % '' for e in ep] + [e % suffix for e in ep]
 
 script_src = """#!{executable}
+# This script was automatically generated by setup.py
 from {mod} import {func}
 {func}()
 """