Handle itemizedlist/listitem/@override

[tgraham-antenna]

Corresponds to what is already implemented for HTML output.

[tgraham-antenna]

I have now found that the 'list.itemsymbol' named template should handle @override. However, @override had no effect with my 1.79.1 stylesheets until I made my change. I don't know what's going wrong where, but this PR may be redundant if 'list.itemsymbol' currently works (though the template appears to no longer be in lists.xsl so I can't be sure).

[bobstayton]

I'm not able to reproduce this problem. When I process this with the stock docbook-xsl-ns-1.79.1/fo/docbook.xsl stylesheet, the @OverRide works and I get a emdash on the first listitem.
<itemizedlist>
<listitem override="emdash"><para>First item with override.</para>
</listitem>
<listitem><para>Second item.</para>
</listitem>
</itemizedlist>

Did you test it with the stock stylesheet or just your customization layer based on 1.79.1?