Fixed a regression introduced in ca3c3a7b56d7c82441e1071a658f3e0537a97d48 where looping over and deleting record-valued keyword cards could, in some cases, result in an exception depending on what order they were deleted in

git-svn-id: http://svn6.assembla.com/svn/pyfits/trunk@2440 ed100bfc-0583-0410-97f2-c26b58777a21
Preparing to re-release v3.1.5 as I did v3.2.2 since the releases were broken and did not contain the intended fixes.
Preparing release 3.1.5
Back to development: 3.1.6