The contents of this attribute are an implementation detail, as
documented for #9442, so we should not parse it, to support non-CPython
VMs in the future.

Unfortunately, one use comes directly from PEP 345, so an edit will have
to be agreed before fixing the code (see comment in d2.markers).

Other remaining uses are found in d2.compiler and could be replaced by
the platform module (which also parses sys.version, but then it wouldn?t
be my fault :)

This should help avoiding issues like #13170.

Because of implicit relative imports, _backport.tarfile already imported
shutil from the backports instead of the stdlib; I have inlined the only
function it needed to remove the circular dependency between these
modules.

I broke test_mixin2to3 somehow; distutils2-default is okay and packaging too,
so I don?t see an obvious reason right now, I?ll investigate later.

This method was named reinitialize_command in distutils and accompanied
by a comment suggesting to change it to get_reinitialized_command.
Following that, I did the change for distutils2, but it proved
confusing: The Distribution object has an internal cache of command
objects, to make sure only one instance is ever used, and the name
get_reinitialized_command could suggest that the object returned was
independent of that cache, which it was not.  I?m reverting the name
change to make code clearer.

I think I?ve got all of them (I?ll clean up compat after); if someone
knows a lint tool that can detect missing super calls, please let me
know.

This codebase is compatible with 3.1, 3.2 and 3.3.  It was converted with 2to3
and a semi-automated diff/merge with packaging in 3.3 to fix some idioms.
We?ve now come full circle from 2.x to 3.x to 2.x to 3.x again :)

Starting from now, contributors can make patches for packaging (preferred, as
the stdlib?s regrtest is very useful), distutils2 or distutils-python3, and
we?ll make patches flow between versions.

There was already a test for this, but it was complicated and had a
subtle bug (custom command objects need to be put in dist.command_obj so
that other command objects may see them) that rendered it moot.

Backports:
- sysconfig is now always imported from our backports
- when hashlib is not found, our backport is used instead of the md5
  module (debatable; we could just drop hashlib)

Version-dependent features:
- PEP 370 features are only enabled for 2.6+
- the check for sys.dont_write_bytecode was fixed to use getattr
  with a default value instead of hasattr

Idioms/syntax:
- octal literals lost their extra 0
- misused try/except blocks have been changed back to try/finally
  (it?s legal in 2.4 too, it?s only try/except/finally that isn?t)
- exception catching uses the regular 2.x idiom instead of sys.exc_info
- file objects are closed within finally blocks (this causes much
  whitespace changes but actually makes diff with packaging easier)

Renamed modules:
- some missed renamings (_thread, Queue, isAlive, urllib.urlsplit, etc.)
  were fixed

Other:
- a few false positive replacements of ?packaging? by ?distutils2? in
  comments or docstrings were reverted
- util.is_packaging regained its name
- assorted whitespace/comment/import changes to match packaging