Argument Clinic: rename "self" to "module" for module-level functions.
Issue #19437: Fix error handling of CDataType_from_buffer()

KeepRef() decreases the reference counter of its 'keep' parameter on error
Issue #19437: Fix error handling of PyCArrayType_new(), don't decreases the
reference counter of stgdict after result stole a reference to it
selectors: use a single return.
Issue #19581: Change the overallocation factor of _PyUnicodeWriter on Windows

On Windows, a factor of 50% gives best performances.
Issue #19513: repr(list) now uses the PyUnicodeWriter API, it is faster than
the PyAccu API
Cleanup this test's modification of os.environ in teardown (this already
exists in 3.4 but apparently wasn't done for 3.3).
null merge (already in 3.4)
Issue #19513: Simplify list_repr()
Issue #19596: Set untestable tests in test_importlib to None
to avoid reporting success on empty tests.
Issue #19596: Null merge with 3.3

This will be merged into default when PEP451 is merged in.  See
changeset 5d38989191bb in features/pep-451