safely together and don't duplicate logic (the common logic was factored
out into new private API function _PySequence_IterContains()).
Visible change:
    some_complex_number  in  some_instance
no longer blows up if some_instance has __getitem__ but neither
__contains__ nor __iter__.  test_iter changed to ensure that remains true.

   but don't plan on actually writing any text until, ooh, say, July or
   thereabouts.

NEEDS DOC CHANGES
A few more AttributeErrors turned into TypeErrors, but in test_contains
this time.
The full story for instance objects is pretty much unexplainable, because
instance_contains() tries its own flavor of iteration-based containment
testing first, and PySequence_Contains doesn't get a chance at it unless
instance_contains() blows up.  A consequence is that
    some_complex_number in some_instance
dies with a TypeError unless some_instance.__class__ defines __iter__ but
does not define __getitem__.

to string.join(), so that when the latter figures out in midstream that
it really needs unicode.join() instead, unicode.join() can actually get
all the sequence elements (i.e., there's no guarantee that the sequence
passed to string.join() can be iterated over *again* by unicode.join(),
so string.join() must not pass on the original sequence object anymore).

because PySequence_Fast() started working for free as soon as
PySequence_Tuple() learned how to work with iterators.  For some reason
unicode.join() still doesn't work, though.

several of these turned up and got fixed during the iteration crusade.

NEEDS DOC CHANGES.
This one surprised me!  While I expected tuple() to be a no-brainer, turns
out it's actually dripping with consequences:
1. It will *allow* the popular PySequence_Fast() to work with any iterable
   object (code for that not yet checked in, but should be trivial).
2. It caused two std tests to fail.  This because some places used
   PyTuple_Sequence() (the C spelling of tuple()) as an indirect way to test
   whether something *is* a sequence.  But tuple() code only looked for the
   existence of sq->item to determine that, and e.g. an instance passed
   that test whether or not it supported the other operations tuple()
   needed (e.g., __len__).  So some things the tests *expected* to fail
   with an AttributeError now fail with a TypeError instead.  This looks
   like an improvement to me; e.g., test_coercion used to produce 559
   TypeErrors and 2 AttributeErrors, and now they're all TypeErrors.  The
   error details are more informative too, because the places calling this
   were *looking* for TypeErrors in order to replace the generic tuple()
   "not a sequence" msg with their own more specific text, and
   AttributeErrors snuck by that.

internals) so clients can be a lot dumber (wrt their knowledge).

free to do one!

NEEDS DOC CHANGES.

NEEDS DOC CHANGES.
Possibly contentious:  The first time s.next() yields StopIteration (for
a given map argument s) is the last time map() *tries* s.next().  That
is, if other sequence args are longer, s will never again contribute
anything but None values to the result, even if trying s.next() again
could yield another result.  This is the same behavior map() used to have
wrt IndexError, so it's the only way to be wholly backward-compatible.
I'm not a fan of letting StopIteration mean "try again later" anyway.

at the same time as it did from PyObject_Init() .

the code necessary to accomplish this is simpler and faster if confined to
the object implementations, so we only do this there.

This causes no behaviorial changes beyond a (very slight) speedup.

void function.

need to be specified in the type structures independently.  The flag
exists only for binary compatibility.

This is a "source cleanliness" issue and introduces no behavioral changes.

NEEDS DOC CHANGES.

    When replacing the exception object, be sure we stuff the new value
    in sys.last_value (which we already did for the original value).

annotations!

Also fixed a typo noted by Neil S.

appropriate next() method, and this is what people really want to do with
these objects in practice.

the support for containers and iteration.

objects but instead assume that they use the requested encoding.

This is needed on Windows to enable opening files by passing in
Unicode file names.

dictionary size was comparing ma_size, the hash table size, which is
always a power of two, rather than ma_used, wich changes on each
insertion or deletion.  Fixed this.

filter() to no longer insist that len(seq) be defined.
NEEDS DOC CHANGES.

Refactored some object initialization to be more reusable.