Fixes #64 by moving the code shared by fromstring and readfrom to an internal method, allowing the public API for fromstring to be simplified.

git-svn-id: http://svn6.assembla.com/svn/pyfits/trunk@2702 ed100bfc-0583-0410-97f2-c26b58777a21
Add izip_longest implementation for python 2.5

git-svn-id: http://svn6.assembla.com/svn/pyfits/trunk@2703 ed100bfc-0583-0410-97f2-c26b58777a21