atlas: make scripts python3 compatible
elliptic_curves: make scripts python3 compatible
zn_poly: run 2to3 on makemakefile.py when using python3
pexpect: run 2to3 when using python3
ipython: add symlink ipython3->ipython when on python3
sage-location: python3 compatible
sage-download-file: python3 compatible
Made tests faster.
Trac #15581: Shorter long tests for KR tableaux and rigged configruations.

As per this thread: https://groups.google.com/forum/?fromgroups=#!topic
/sage-combinat-devel/WMk7H-J65qE

__The technical reasoning__:

In #13872, I implemented `e0` and `f0` operators for KR tableaux and
rigged configurations by mapping to their corresponding
`KirillovReshetikhinCrystal` element, then applying `e0` and `f0`
(respecitvely) there, and then pulling back. Previously they just
returned `None`. In `_test_stembridge_local_axioms()`, it checks to see
that `e(i)` and `e(j)` are both not `None`, which now there is a longer
check if that's true, and if so, then it must perform the Stembridge
axioms check. This is why the tests now take significantly longer than
before.

__The proposed solution__:

Make the crystals smaller.

URL: http://trac.sagemath.org/15581
Reported by: tscrim
Ticket author(s): Travis Scrimshaw
Reviewer(s): Volker Braun
Trac #15540: trivial pkg fixes needed for python3

The following 5 packages either don't install or create a broken install
when using python3, and are trivial to fix:

1. atlas
1. ipython
1. pexpect
1. zn_poly
1. elliptic_curves

URL: http://trac.sagemath.org/15540
Reported by: ohanar
Ticket author(s): R. Andrew Ohana
Reviewer(s): Volker Braun
Trac #15541: sage-location and sage-download-file are broken with python3

Obviously other sage scripts will need updating, but these are probably
the ones that get you into trouble quite early on.

URL: http://trac.sagemath.org/15541
Reported by: ohanar
Ticket author(s): R. Andrew Ohana
Reviewer(s): Volker Braun