Close #20053: ignore default pip config settings

ensurepip now sets PIP_CONFIG_FILE to os.devnull before
import pip from the wheel file. This also ensures venv
ignores the default settings when bootstrapping pip.
restore namespacing of pyexpat symbols (closes #19186)
merge 3.3 (#19186)
Issue #20509: Added cross-reference in documentation.
Closes #20509: Merged documentation update from 3.3.
asyncio doc: add an example to schedule a coroutine from a different thread
Add missing word ("thread") to sentence about call_soon_threadsafe.
asyncio: Cosmetic improvement to test__run_once_logging() mock argument.
Issue #20515: Fix NULL pointer dereference introduced by issue #20368
CID 1167595
Issue #20515: Fix NULL pointer dereference introduced by issue #20368
CID 1167595
Issue #20465: Update SQLite shipped with OS X installer to 3.8.3.
Issue #20489: Explicitly qualified expressions for default values in methods.
Issue #20498: Fixed io.StringIO tests for newline='\n'. Added new tests.
Issue #20498: Fixed io.StringIO tests for newline='\n'. Added new tests.
Issue #20053: new test to check an assumption
TestNamedTuple.test_pickle was only testing through protocol 2. Changed to have it automatically test through the most recent version.
Issue #19920: TarFile.list() no longer fails when outputs a listing
containing non-encodable characters.  Added tests for TarFile.list().
Based on patch by Vajrasky Kok.
Issue #19920: TarFile.list() no longer fails when outputs a listing
containing non-encodable characters.  Added tests for TarFile.list().
Based on patch by Vajrasky Kok.
#14515: clarify that TemporaryDirectory's __enter__ returns the name.
#14515: clarify that TemporaryDirectory's __enter__ returns the name.