to NULL during the lifetime of the object.

* listobject.c nevertheless did not conform to the other invariants,
  either; fixed.

* listobject.c now uses list_clear() as the obvious internal way to clear
  a list, instead of abusing list_ass_slice() for that.  It makes it easier
  to enforce the invariant about ob_item == NULL.

* listsort() sets allocated to -1 during sort; any mutation will set it
  to a value >= 0, so it is a safe way to detect mutation.  A negative
  value for allocated does not cause a problem elsewhere currently.
  test_sort.py has a new test for this fix.

* listsort() leak: if items were added to the list during the sort, AND if
  these items had a __del__ that puts still more stuff into the list,
  then this more stuff (and the PyObject** array to hold them) were
  overridden at the end of listsort() and never released.

* Use plain wording in docs for id().
* Use normal quotation marks instead of single quotes in the description.

mutation during list.sort() used to rely on that listobject.c always
NULL'ed ob_item when ob_size fell to 0.  That's no longer true, so the
test for list mutation during a sort is no longer reliable.  Changed the
test to rely instead on that listobject.c now never NULLs-out ob_item
after (if ever) ob_item gets a non-NULL value.  This new assumption is
also documented now, as a required invariant in listobject.h.

The new assumption allowed some real simplification to some of the
hairier code in listsort(), so is a Good Thing on that count.

Backport candidate.

invariants they must satisfy.

the size_t nbytes, and passed nbytes to malloc, so it was confusing to
effectively recompute the same thing from scratch in the memset call.

Py_RETURN_FALSE and Py_RETURN_TRUE.

can contain more than just .py files.  Make sure we only report
bytecode files for the .py files.

versionadded{} args quite right).

for it soon.

aren't intended to be part of Python distributiuon.  This was
accidently imported on mass converting from standalone version of
CJKCodecs.

apply os.fsync() to the GzipFile backup files it creates.

Will backport to 2.3.

for people using floor(), ceil() and modf().

Clarifed that os.environ is captured once; emphasized that it's better
to assign to os.environ than to call putenv() directly (the putenv()
docs said so, but the environ docs didn't).