man: skip directive starting with ".."

man: skip directive starting with ".."

the target definition of hyper link looks like:

.. _a-reference-label:

there is chance that we need to add `:ref:` referencing man pages,
and add target definition at the beginning of the manapges for the
references. in that case, we need to skip the ref directives when
looking for the title of the manpage.

Signed-off-by: Kefu Chai <kchai@redhat.com>