Exclude empty checksums from export

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@22947 4ae1f11a-8b86-4847-b8af-ab372f36d1fd
flags HAS_CLIMERGE and HAS_EXPORTRAW to skip tests

Thanks, Nick!

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@22948 4ae1f11a-8b86-4847-b8af-ab372f36d1fd