Add Python 3.4 to tox.ini

git-svn-id: http://svn6.assembla.com/svn/pyfits/trunk@2721 ed100bfc-0583-0410-97f2-c26b58777a21
Backport fixes needed for Python 3.4 from Astropy

git-svn-id: http://svn6.assembla.com/svn/pyfits/trunk@2722 ed100bfc-0583-0410-97f2-c26b58777a21