Merge with 3.4: Issue #24259: tarfile now raises a ReadError if an archive is truncated inside a data segment.

on OS X.  Original patch by André Freitas.

Remove build condition to prevent old strings hanging around
Add -h option to build.bat

- update installer ReadMe file
- suppress installer per-file byte-compilation messages to system log
- speed up installer byte-compilation
- isolate ensurepip install from user site-packages

collections.abc.Awaitable and collections.abc.Coroutine no longer
use __instancecheck__ hook to detect generator-based coroutines.

inspect.isawaitable() can be used to detect generator-based coroutines
and to distinguish them from regular generator objects.

Fixes warnings when building python3.dll due to the .def file accumulating multiple copies of each line.
Adds shebang line to prepare_ssl so it will run with py.exe.

Patch by Petr Viktorin.