MediaWiki upgrade to 1.19.0 regression

Upgrade from an earlier version to 1.19.0 breaks some installations, with error:

"Revision::fetchFromConds". Database returned error "1054:
Unknown column 'rev_sha1' in 'field list' (localhost)".

This has been reported as a bug, and fixed in the development branch. Temporary fixes: downgrade back to 1.18.3 (tar.gz) or upgrade to a snapshot of the master branch of 1.20alpha.