GeezerVison

…er shutdown code

Fix the implementation to work as documented if a thread dies. Now
Stackless kills only tasklets with a nesting level > 0. During interpreter
shutdown stackless additionally kills daemon threads, if they execute Python code or
switch tasklets. This prevents access violations after clearing the thread states.

Add a 1ms sleep for each daemon thread. This way the thread gets a better
chance to run. Thanks to Kristján Valur Jónsson for suggesting this improvement.

Add a test case for a C assertion violation during thread shutdown.
Add some explanatory comments to the shutdown test case.
Thanks to Christian Tismer for the sugestion.

https://bitbucket.org/stackless-dev/stackless/issues/81
https://bitbucket.org/stackless-dev/stackless/issues/89
(grafted from 2cc41427a347a1ebec4eedc3db06a3664e67f798, 1388a2003957,
6140f5aaca2c and edc9b92ec457)

…er versions of Python 3.

The 2.7 detector hook (cleanup of codecs search path) does not work with Python 3.3 and later.
Adapt the test cases to use a different hook (builtins._).

…during shutdown

Since issue python#81 Stackless 2.7 raises TaskletExit in daemon threads during interpreter shutdown.
This prevents later crashes (i.e. segfaults). In Python 3 this precautions are no longer required
and break the CPython test case test.test_threading.ThreadJoinOnShutdown.test_6_daemon_threads.
This changeset removes the code, that raises TaskletExit.