In C++, it's an error to pass a string literal to a char* function
without a const_cast().  Rather than require every C++ extension
module to put a cast around string literals, fix the API to state the
const-ness.

I focused on parts of the API where people usually pass literals:
PyArg_ParseTuple() and friends, Py_BuildValue(), PyMethodDef, the type
slots, etc.  Predictably, there were a large set of functions that
needed to be fixed as a result of these changes.  The most pervasive
change was to make the keyword args list passed to
PyArg_ParseTupleAndKewords() to be a const char *kwlist[].

One cast was required as a result of the changes:  A type object
mallocs the memory for its tp_doc slot and later frees it.
PyTypeObject says that tp_doc is const char *; but if the type was
created by type_new(), we know it is safe to cast to char *.

(fixes bug #1119418)

* Have groupby() be careful about decreffing structure members.

(Contributed by Dima Dorfman)

Both cycle() and chain() were handling exceptions only when switching
input sources.  The patch makes the handle more immediate.

Will backport.

instead of %d .

ifilterfalse().

Original idea by Guido van Rossum.
Idea for skipable inner iterators by Raymond Hettinger.
Idea for argument order and identity function default by Alex Martelli.
Implementation by Hye-Shik Chang (with tweaks by Raymond Hettinger).

Formerly, underlying queue was implemented in terms of two lists.  The
new queue is a series of singly-linked fixed length lists.

The new implementation runs much faster, supports multi-way tees, and
allows tees of tees without additional memory costs.

The root ideas for this structure were contributed by Andrew Koenig
and Guido van Rossum.

* tee object is no longer subclassable
* independent iterators renamed to "itertools.tee_iterator"
* fixed doc string typo and added entry in the module doc string

* Add error checking code to PyList_Append() call.

* Replace PyObject_CallMethod(to->outbasket, "pop", NULL) with equivalent
  in-line code.  Inlining is important here because the search for the
  pop method will occur for every element returned by the iterator.

* Make tee's dealloc() a little smarter.  If the trailing iterator is
  being deallocated, then the queue data is no longer needed and can
  be freed.

It works like the pure python verion except:
* it stops storing data after of the iterators gets deallocated
* the data queue is implemented with two stacks instead of one dictionary.

Avoid Armin Rigo's dastardly exercise in re-entrancy.

which can now take zero arguments.

(Contributed by Andrew I MacIntyre.)

* Updated comment on design of imap()
* Added untraversed object in izip() structure
* Replaced the pairwise() example with a more general window() example

  the itertoolsmodule.
* Taught itertools.repeat(obj, n) to treat negative repeat counts as
  zero.  This behavior matches that for sequences and prevents
  infinite loops.

It is better to be explicit and just allow stop to be None.

* itertools.islice() stop argument did not perform as documented.
* beefed-up test suite

to more accurately describe what the function does.

Suggested by Thomas Wouters.

Factors out the common case of returning self.

Subsumed times() into repeat().
Added cycle() and chain().

* Removed the ifilter flag wart by splitting it into two simpler functions.
* Fixed comment tabbing in C code.
* Factored module start-up code into a loop.

Documentation:
* Re-wrote introduction.
* Addede examples for quantifiers.
* Simplified python equivalent for islice().
* Documented split of ifilter().

Sets.py:
* Replace old ifilter() usage with new.