Changed previous recommendation header

Now Matches best practice according to W3C pubs.  Uses 'Recommendation'
instead of 'recommendation' and shows 'Previous Recommendation' if
status is REC and there was a previous REC.  These changes at the
request of Ivan Herman and backed up by evidence in a non-ReSpec
produced recent W3C Recommendation at
http://www.w3.org/TR/2013/REC-rdf-sparql-XMLres-20130321/