Add missing verb ("is")

git-svn-id: http://svn6.assembla.com/svn/pyfits/trunk@2248 ed100bfc-0583-0410-97f2-c26b58777a21
Fix misspelled word ("Deletetion")

Conflicts:

	lib/pyfits/header.py

git-svn-id: http://svn6.assembla.com/svn/pyfits/trunk@2251 ed100bfc-0583-0410-97f2-c26b58777a21