Clarify the subprocess documentation.

I noticed this had slipped into the original commit when
resolving a merge conflict for the backport to 3.7.

Historically, -m added the empty string as sys.path
zero, meaning it resolved imports against the current
working directory, the same way -c and the interactive
prompt do.

This changes the sys.path initialisation to add the
*starting* working directory as sys.path[0] instead,
such that changes to the working directory while the
program is running will have no effect on imports
when using the -m switch.

- new test case for pre-initialization of sys.warnoptions and sys._xoptions
- restored ability to call these APIs prior to Py_Initialize
- updated the docs for the affected APIs to make it clear they can be
  called before Py_Initialize
- also enhanced the existing embedding test cases
  to check for expected settings in the sys module

Harden ssl module against LibreSSL CVE-2018-8970.
X509_VERIFY_PARAM_set1_host() is called with an explicit namelen. A new test
ensures that NULL bytes are not allowed.
Signed-off-by: Christian Heimes <christian@python.org>

bpo-33134: dataclasses: use function dispatch table for hash, instead of a string lookup which then is tested with if tests. (GH-6222)

* Change _hash_action to be a function table lookup, instead of a list
of strings which is then tested with if statements.

- When adding a single element to a list, use .append() instead of
  += and creating a new list.
- For consistency, import the copy module, instead of just deepcopy. This
  leaves only a module at the class level, instead of a function.
- Improve some comments.
- Improve some whitespace.
- Use tuples instead of lists.
- Simplify a test.

LibreSSL 2.7 introduced OpenSSL 1.1.0 API. The ssl module now detects
LibreSSL 2.7 and only provides API shims for OpenSSL < 1.1.0 and
LibreSSL < 2.7.

Documentation updates and fixes for failing tests will be provided in
another patch set.
Signed-off-by: Christian Heimes <christian@python.org>

Commit 141c5e8c re-added match_hostname() call. The resurrection of the
function call was never intended and was solely a merge mistake.
Signed-off-by: Christian Heimes <christian@python.org>

Reported by Maksym Nikulyak on docs.p.o.

into/out of an except block.

* Added new opcode END_ASYNC_FOR.
* Setting global StopAsyncIteration no longer breaks "async for" loops.
* Jumping into an "async for" loop is now disabled.
* Jumping out of an "async for" loop no longer corrupts the stack.
* Simplify the compiler.

bpo-32505: dataclasses: raise TypeError if a member variable is of type Field, but doesn't have a type annotation. (GH-6192)

If a dataclass has a member variable that's of type Field, but it doesn't have a type annotation, raise TypeError.

bpo-33018 (GH-5944) fixed bpo-32999 too.  So fc7df0e6 is not required
anymore.  Revert it except test case.

This improves error message for situations when a non-class is
checked w.r.t. an abstract base class.

- Add missing 'Field' to __all__.
- Improve tests to catch this.

bpo-32896: Fix error when subclassing a dataclass with a field that uses a default_factory (GH-6170)

Fix the way that new annotations in a class are detected.

The result of host() was not empty when the network is constructed by a tuple containing an
integer mask and only 1 bit left for addresses.

Original patch by Jon Foster and Berker Peksag.

If the class has a member that's a MemberDescriptorType, it's not a default value, it's from that member being in __slots__.

If a non-dataclass derives from a frozen dataclass, allow attributes to be set.
Require either all of the dataclasses in a class hierarchy to be frozen, or all non-frozen.
Store `@dataclass` parameters on the class object under `__dataclass_params__`. This is needed to detect frozen base classes.

This reverts commit ac317700.

(Reverts only the lib2to3 part.)