The following produces an ndash rather than two hyphens, using db2ps:

<!DOCTYPE para PUBLIC "-//OASIS//DTD DocBook V3.1//EN"[]>
<para>
 <programlisting>
  <![CDATA[count--;]]>
 </programlisting>
</para>

The work-around that I'm using is this:

<!DOCTYPE para PUBLIC "-//OASIS//DTD DocBook V3.1//EN"[]>
<para>
 <programlisting>
  <![CDATA[count]]>&mdash;<![CDATA[;]]>
 </programlisting>
</para>

(Obviously it can be done more simply for this small example)

This is a bug in jade since it puts '--' in the TeX output, which of course
is TeX speak for ndash.  It doesn't seem reasonable to do this when in
<programlisting><![CDATA[[...]]></> tags. (I don't fully understand why
&mdash; comes out as two dashes rather than an mdash, either, but at least
it gives me a work-around..)