#196 Support expending properties in refid attributes.

[Frederic Jean]

I'm using the zip task and I have a dynamic list of fileset and i think it would be a great feature to support property expanding in attributes like refid.

<zip zipfile = "${__zipfile}" includeemptydirs = "true" verbose = "true" >
<fileset refid = "${__artifact_refid}" />
<fileset>
<include name = "${__manifest_xml}" />
</fileset>
</zip>