Fixed shadowing of jQuery referenced by a global ``jQuery`` variable by ``django.jQuery``
in the tabbed admin script.

Javascript has a nasty semantic of moving initializers to the beginning of a block, thus
rewritting ``var a = a || b`` as ``var a; a = a || b``. With such a code, if ``a`` starts
as a global variable with some value, you could think that it would end up having the same
value, but it is actually first set to ``undefined`` at the beginning of the block and
then always set to ``b`` in the statement [1][2].

This is mostly of importance if you actually have more than one jQuery loaded.
For instance, this happens with Mezzanine -- first Grappelli-safe loads a copy, and calls
``$.noConflict`` thus storing its version as ``jQuery``, second is Django, loading another
copy and calling ``django.jQuery = jQuery.noConflict(true)``. So far so good, we have one
copy on ``jQuery`` and another on ``django.jQuery``; jQuery UI chooses to load itself onto
the ``jQuery`` (Grappelli) copy. But now runs the tabbed_translation_fields script, hiding
the jQuery with UI loaded at the very beggining of the first block, and a moment later
complaining that ``.tabs()`` or something else is not defined.

[1]: http://www.ecma-international.org/ecma-262/5.1/#sec-12.2 (note the first paragraph after the grammar)
[2]: http://stackoverflow.com/questions/500431/what-is-the-scope-of-variables-in-javascript (point 8)
A more elegant solution suggested by zlorf.
Merge pull request #267 from wrwrwr/fix-tabbed-admin-with-two-jqueries

Make tabbed admin work with two jQueries (fixed javascript scoping issue).