rename some table header functions

git-svn-id: svn+ssh://svn.abisource.com/svnroot/abiword/branches/gsoc2013tables@33338 bcba8976-2d24-0410-9c9c-aab3bd5fdfd6
refactor the table header code

git-svn-id: svn+ssh://svn.abisource.com/svnroot/abiword/branches/gsoc2013tables@33339 bcba8976-2d24-0410-9c9c-aab3bd5fdfd6