Fix for issue #49

git-svn-id: http://svn6.assembla.com/svn/pyfits/trunk@2505 ed100bfc-0583-0410-97f2-c26b58777a21
Record this fix in the changelog for 3.1 as well.

git-svn-id: http://svn6.assembla.com/svn/pyfits/trunk@2506 ed100bfc-0583-0410-97f2-c26b58777a21