Fix usage of support.import_module('asyncio'): store the result in an 'asyncio'
variable.

Skip test_asyncio_1() when the asyncio module cannot be imported because
CPython is compiled with no thread support.

Add "#ifdef WITH_THREAD" around cals to:

* PyGILState_Check()
* _PyImport_AcquireLock()
* _PyImport_ReleaseLock()

Patch by Nir Soffer.

This reuses existing code to hopefully make the new test_input_no_stdout_
fileno() test work. It is hanging Free BSD 9 and OS X Tiger buildbots, and I
don't know why.

Also add to comment in the C code.

Also factored out some test cases into a new PtyTests class.

sys.path has an unwritable __pycache__ directory.

This typically comes up when someone runs the test suite from an
administrative install of Python on Windows where the user does not
have write permissions to the stdlib's directory.

Thanks to Zachary Ware and Matthias Klose for reporting bugs related
to this issue.
(grafted from 34bbd537b3e688dfbb6498e9083445a6a72fc4b1)

sys.path has an unwritable __pycache__ directory.

This typically comes up when someone runs the test suite from an
administrative install of Python on Windows where the user does not
have write permissions to the stdlib's directory.

Thanks to Zachary Ware and Matthias Klose for reporting bugs related
to this issue.

This is a relatively benign bug, since having both be true was correctly
rejected at in SMTPServer even before this patch.

Patch by Xiang Zhang.

Patch by Henrik Heimbuerger and Bar Harel.

Patch by Henrik Heimbuerger and Bar Harel.