Issue #25274: sys.setrecursionlimit() now raises a RecursionError if the new
recursion limit is too low depending at the current recursion depth. Modify
also the "lower-water mark" formula to make it monotonic. This mark is used to
decide when the overflowed flag of the thread state is reset.

condition in test_eintr.

the other buttons and the new IDLE Dark theme.

Otherwise, stray registry entries would cause issues.
Also fixes an accelerator collision and improves UAC icons when upgrading.

already supports reduce protocol 4 (issue #20289).

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.