Fix closes Issue12183 - Explain the Symlink copy behavior in shutil.copytree. Patch by Petri Lehtinen.

Reported by Popa Claudiu and Patch by Santoso Wijaya.

Reported by Popa Claudiu and Patch by Santoso Wijaya.

Also, add an entry for the script in Tools/scripts/README.

Issue #11049: fix test_forget to work on installed Python, by using a temporary module for import/forget

See: https://bugzilla.redhat.com/show_bug.cgi?id=726536

This will be particularly useful to Windows users.

run_tests.py originally written by Brett Cannon.