This continues 6b4990f6 (gpython: Fix pymain to properly setup
sys.path) - now we add test and verify that gpython actually sets
sys.path in the same way as underlying python does:
- don't add directory of gpython to sys.path
- for `gpython file` add to sys.path realpath(dir(file)) instead of
dir(file) (see PySys_SetArgvEx for the reference, and else - if we do
not make this change - added test breaks)
- for `gpython -m mod` add to sys.path realpath('') instead of ''.
This exactly matches PY3 behaviour, while PY2 behaviour is to add ''
However PY3 behaviour
* is more sane, and
* fixes test_defer_excchain_traceback on py27-gevent
-> so we stick to it.
Now all tests pass again.