125044: - use field's content cache on <SwTxtFld> construction only for clipboard documents
        - assure invalidation and updates on code to update fields

	cherry-picked from trunk



git-svn-id: https://svn.apache.org/repos/asf/openoffice/branches/AOO410@1603723 13f79535-47bb-0310-9956-ffa450edef68