Fix python3 issues in some examples

Unfortunately these are the easy ones ...

This mostly involves intervals/keys and xrange. For the most part I chose simplicity over minimising memory usage and replaced interkeys etc. with keys. The loops are rather short so the benefits from iterators is rather limited. If anyone thinks it is important I am happy to change this.
Fair enough.  At this point I think of six as being part of the 'standard'
library and don't write anything without it so did not give it a tremendous
amount of thought.

The case could be made that the examples are should also be examples of
general best practices, and python 2/3 compatibility is one of them, but I
will defer to your judgement on this.

On Tue Nov 25 2014 at 3:40:52 PM Jens Hedegaard Nielsen <
notifications@github.com> wrote:

> In doc/pyplots/whats_new_99_spines.py:
>
> > @@ -4,7 +4,7 @@
> >
> >
> >  def adjust_spines(ax,spines):
> > -    for loc, spine in ax.spines.iteritems():
> > +    for loc, spine in ax.spines.items():
>
> I deliberately chose to avoid six as much as possible to simplify the
> examples. As I see it examples has a different balance between code
> readability and performance. But you are probably right that in the cases
> of axes spines etc. which are somewhat longer loops it makes sense to use
> iterators.
>
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