Issue #8674: fix another bogus overflow check in audioop module.

Issue #8674: Fix incorrect and UB-inducing overflow checks in audioop
module.  Thanks Tomas Hoger for the patch.

fixes local subclasses leaving old state around after a ref cycle GC which
could be recycled by new locals
(backported from r75123)

old behavior).

forever on incomplete input. That caused tarfile.open() to hang when used
with mode 'r' or 'r:bz2' and a fileobj argument that contained no data or
partial bzip2 compressed data.

(backported from r70523)

See issue #5389.

Added test case to ensure attempts to read from a file opened for writing
fail.

EOF was hit.

Issue #4342: Always convert Text.index result to string.

Issue #1683: prevent forking from interfering in threading storage.

Issue #3863: Disabled a unit test of fork being called from a thread
when running on platforms known to exhibit OS bugs when attempting that.