Bug 1401210. The get_artefacts() method is used by the Blogpost
artefact to find all the blocks that use a particular blogpost,
for storing in the view_artefacts table.

This one was skipping the blogposts themselves, and it was
including content from unpublished blog entries.

Change-Id: I4248be998ba4082722648a1ddbcf1c9334672409