Issue #18080: When building a C extension module on OS X, if the compiler
is overriden with the CC environment variable, use the new compiler as
the default for linking if LDSHARED is not also overriden.  This restores
Distutils behavior introduced in 3.2.3 and inadvertently dropped in 3.3.0.
Issue #15392: Do not run tests if threading/_thread not available. Otherwise
touchup test_idle. Rename README.txt.
#17403: urllib.parse.robotparser normalizes the urls before adding to ruleline.
This helps in handling certain types invalid urls in a conservative manner.
Issue #17768: Support newline fill character in decimal.py and NUL fill
character in _decimal.c.
Backport bff16086f03b and bcaaaa00425b.
Support multiarch build in tests.