Multiple fixes including one by mgorny for a race condition that breaks dev-python/psycopg-2.7.3.2[doc] for me. Simply renaming dev-python/sphinx-1.6.3-r3 seems fine.
While we are at it - it looks like 1.6.7 has been released: http://www.sphinx-doc.org/en/master/changes.html#release-1-6-7-released-feb-04-2018
1.6.7 has been committed