INSERT IGNORE when inserting NULL into a non-nullable field will succeed
with a warning on MySQL but fail on PostgreSQL. In any case, it's
probably harmful and unintended. But to check the error code of MySQL
warnings, you need to query the server with SHOW WARNINGS, so there is a
performance cost.
So, add a configuration variable which, when enabled, checks warnings
after INSERT to see if there were any null type constraint errors. Set
it to true in DevelopmentSettings.php and TestSetup.php.
Change-Id: I5e47e2d3cc7e0f804036e11b512b1e3b76804432
551ec29ea6