Preparing release 3.1.5

git-svn-id: http://svn6.assembla.com/svn/pyfits/branches/3.1-stable@2621 ed100bfc-0583-0410-97f2-c26b58777a21
Back to development: 3.1.6

git-svn-id: http://svn6.assembla.com/svn/pyfits/branches/3.1-stable@2622 ed100bfc-0583-0410-97f2-c26b58777a21