Issue 558: Data from private external tenants should not pop up in search results.
Issue 558: Filter out data in related content searches that originates from private tenants.
Data from private external tenants should not appear in related content searches.
Merge branch 'issue-558-external-searches' of git://github.com/simong/Hilary into issue-558-external-searches
Documentation follow-up
Added sanity checks in unit tests + documentation.
Merge branch 'master' into issue-558-external-searches
Merge branch 'issue-558-external-searches' of git://github.com/simong/Hilary into issue-558-external-searches

Conflicts:
	node_modules/oae-content/lib/searches/relatedcontent.js
	node_modules/oae-search/lib/searches/general.js