Fixes #59

Conflicts:

	lib/pyfits/header.py

git-svn-id: http://svn6.assembla.com/svn/pyfits/branches/3.2-stable@2685 ed100bfc-0583-0410-97f2-c26b58777a21
Fixes #58 with a special case to prevent duplicate insertion of commentary keywords

git-svn-id: http://svn6.assembla.com/svn/pyfits/branches/3.2-stable@2686 ed100bfc-0583-0410-97f2-c26b58777a21