Merge pull request #46 from embray/issue-46

FITS File Writing Performance

git-svn-id: http://svn6.assembla.com/svn/pyfits/branches/3.2-stable@2415 ed100bfc-0583-0410-97f2-c26b58777a21
Add changelog entry for #46; I also decided not to backport it to 3.0.x as most of the changes won't apply well to the old Header code in that branch, and it's not really a bug fix anyways.

git-svn-id: http://svn6.assembla.com/svn/pyfits/branches/3.2-stable@2416 ed100bfc-0583-0410-97f2-c26b58777a21