#96 RD: support plural terms

[Rob Bodington]

We have introduced {activity http://docs.oasis-open.org/ns/plcs/plcs#Activity\}
as a way of referencing a term/owl class
The XSL will display this as a preferred label hyperlinked to the owl class
We need a way of using plurals.
For example "activities"

It is proposed to extend the reference with :PLURAL
{activities http://docs.oasis-open.org/ns/plcs/plcs#Activities\}

This requires that the plural of the preferred term is stored.

It is proposed to use the dc:alternative for this

[Rob Bodington]

Checking in xsl/refdata/rdl_owl_definitions.xsl;
/cvsroot/plcslib/plcslib/xsl/refdata/rdl_owl_definitions.xsl,v <-- rdl_owl_definitions.xsl
new revision: 1.9; previous revision: 1.8
done
Checking in xsl/refdata/rdl_common.xsl;
/cvsroot/plcslib/plcslib/xsl/refdata/rdl_common.xsl,v <-- rdl_common.xsl
new revision: 1.6; previous revision: 1.5
done
Checking in xsl/common.xsl;
/cvsroot/plcslib/plcslib/xsl/common.xsl,v <-- common.xsl
new revision: 1.24; previous revision: 1.23