v5 adds test cases for sys.executable and calls realpath on dirname(argv[0]) in pythonw.c and also has the changes in Ned's v4.

The test failure for test_venv is expected, the note in <http://docs.python.org/dev/library/venv.html> explains that "sys.base_prefix and sys.base_exec_prefix point to the non-venv Python installation which was used to create the venv". The test fails because it assumes that sys.base_prefix of the created venv is same as sys.prefix of the running python, which is not true when you create a venv in a venv.

In particular line 95 of test_venv explicitly tests that sys.prefix == sys.base_prefix, which should fail when running the test within a virtual env. Tweaking the test suite to avoid that failure is beyond the scope of this issue.