Lib/imp.py.

defined in sysmodule.c instead of straight out of a Unicode object.

Thanks to Amaury Forgeot d'Arc for noticing the bug and Eric Snow for
writing the patch.

Add a note about pkgutil and how some things do not work in the face of PEP 302 permeating throughout import.

longer work as expected in Python 3.3 as importlib's loaders do not
implement the non-standard iter_modules() method. Also link to the
term "loader" in the requisite notes to help make it clearer what has
happened.

NotimplementedError when sys.implementation.cache_tag is None.

Thanks to Pranav Ravichandran for taking an initial stab at the patch.

importlib._bootstrap in imp to fix a grammatical mistake.

Thanks to Marc Abramowitz for the patch.

execfile().

Closes #15281, #15283: Don't make venv scripts executable, but copy source mode instead, and provide better help for pyvenv.