Fix a Python 3 incompatibility that was introduced by the fix for #48 (which was written before the switchover to unified codebase)

git-svn-id: http://svn6.assembla.com/svn/pyfits/trunk@2540 ed100bfc-0583-0410-97f2-c26b58777a21
Add a new is_blank attribute to Cards; simplify checking cards and minimize cases where new cards added to headers need to have their images generated

git-svn-id: http://svn6.assembla.com/svn/pyfits/trunk@2545 ed100bfc-0583-0410-97f2-c26b58777a21
A changelog entry for this new API feature

git-svn-id: http://svn6.assembla.com/svn/pyfits/trunk@2546 ed100bfc-0583-0410-97f2-c26b58777a21
include docstring for is_blank

git-svn-id: http://svn6.assembla.com/svn/pyfits/trunk@2547 ed100bfc-0583-0410-97f2-c26b58777a21
Squashed commit of the following:

commit 17fbac04ad978126d771f4c37529a2ccb89f676a
Author: Erik M. Bray <embray@stsci.edu>
Date:   Sat Feb 1 14:10:38 2014 -0500

    A changelog entry for the first fix for #37

commit b70a24de89fad2487ade6e854162f004726cdb75
Author: Erik M. Bray <embray@stsci.edu>
Date:   Sat Feb 1 14:09:04 2014 -0500

    Fix the first issue related to spacetelescope/PyFITS#37, that Python 2 was allowing non-ASCII strs to be assigned as Header values

git-svn-id: http://svn6.assembla.com/svn/pyfits/trunk@2548 ed100bfc-0583-0410-97f2-c26b58777a21
Squashed commit of the following:

commit e609bd9568e3b8e8d958c51d522f6eac8c9bc58e
Author: Erik M. Bray <embray@stsci.edu>
Date:   Wed Feb 5 19:15:44 2014 -0500

    This gets the remaining basic uses cases for updating a compressed image header properly synchronizing with the table header.  This adds quite a bit of complexity that I was trying to avoid, but it's really necessary under the current design.  Also moved all the compressed image tests into their own class for better organization.

commit c7673a66c815eb30458c7f3f02a2a44ad0a7c7a4
Author: Erik M. Bray <embray@stsci.edu>
Date:   Wed Feb 5 13:54:58 2014 -0500

    Implemented (correctly, I hope) deletion on CompImageHeaders.  This also allowed some cleaning up and simplification of CompImageHDU.header

commit c7492d14658295781e4cc930513df9bbf51a3a6d
Author: Erik M. Bray <embray@stsci.edu>
Date:   Wed Feb 5 12:11:02 2014 -0500

    Not sure what the deal is, but something has changed/broken in coverage.py and now it is weirdly including a few stdlib modules in the report unless I specify this

commit 034c79b962dace08c9ebfc28a5b65fe9f36f8749
Author: Erik M. Bray <embray@stsci.edu>
Date:   Wed Feb 5 11:29:21 2014 -0500

    Progress toward improved synchronization between the fake ImageHDU header and the underlying table header for compressed images.  I still want to rewrite CompImageHDU to be a subclass of ImageHDU to begin with, which will simplify the code tremendously.  But in the meantime this is at least better and more consistent.  Still a little more work needs to be done so that __delitem__ and insertions are working correctly but this is better than it was.

commit 51338ea42e930ace1e2948085aa58312ab1283c2
Author: Erik M. Bray <embray@stsci.edu>
Date:   Tue Feb 4 19:15:50 2014 -0500

    Fix a small bug I noticed trying to iterate over a dict

git-svn-id: http://svn6.assembla.com/svn/pyfits/trunk@2550 ed100bfc-0583-0410-97f2-c26b58777a21