validator: fix bugs in checking character content in foreign elements

See ODF 1.2 section 3.17 Foreign Elements and Attributes.

In particular, for ODF 1.2 it was not actually checked whether an
ancestor is a <text:p>/<text:h> element (which is where it differs from
ODF 1.1).

git-svn-id: https://svn.apache.org/repos/asf/incubator/odf/trunk@1643200 13f79535-47bb-0310-9956-ffa450edef68