This patch adds a new zipiterobject type to
iterobject.c so that we do not import itertools.izip to
do our iterative zip.

There is test_zip.py added that is a stripped down
version of the itertools test.

It's my first patch so go easy on me. ;)

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I get a fatal error on the DECREF(ro) call at line 419 of
iterobject.c.  Investigating...

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Deleting that line (line 419) fixes the problem.  Then all
tests pass.  The patch has small style issues though, and
I'm not sure whether the zip iter ought to have a
__length_hint__ method at all.

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Removed the __length_hint__ stuff which clears up the
uninitialized ro which caused the seg fault.
Changed zip_create_iter to _PyZip_Create.
Added result into zipiter_traverse and zipiter_dealloc.

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I've made some small changes and checked it in (r51620):

- fixed a few odd whitespace cases, e.g.
    for(i=0 ;
  into
    for (i = 0;

- disabled the specific type error

- rearranged the code so the type object is last;
  this reduces the number of forward decls needed

- shortened a long line