Solr Join: Return Parent and Child Documents

Solr JoinQParserPlugin returns only right side(parent) documents, it would be great if we can return all documents.

User case:
If JoinQParserPlugin can return all (parent and child) documents, client can group parent and child docs together with same group.field - (optionally) then use group.main=true to navigate them.

The implementation in single mode:
(as solr join doesn't support distributed search)

req parameter:

{!join from=man_id to=id includeParent=true}

Add includeParent into org.apache.solr.search.JoinQuery
Update JoinQuery's hashCode and equals to include includeParent.

In org.apache.solr.search.JoinQuery.JoinQueryWeight.getDocSet()
DocSet fromSet = fromSearcher.getDocSet(q);

if (includeParent) {
rstDocset = rstDocset.union(fromSet);
}