Philippe Pepiot <philippe.pepiot@logilab.fr> [Wed, 08 Feb 2017 10:31:26 +0100] rev 11954
Make load_module() return existing module if present in sys.modules
Otherwise the reload() builtin will not work correctly:
https://www.python.org/dev/peps/pep-0302/#specification-part-1-the-importer-protocol