Fixes spacetelescope/PyFITS#6; although the specifications of the HIERARCH convention don't say anything about leading whitespace, CFITSIO's behavior is to strip it, and that is probably the expected behavior by most people.

git-svn-id: http://svn6.assembla.com/svn/pyfits/trunk@2153 ed100bfc-0583-0410-97f2-c26b58777a21