Avoid master queries in Revision::newFromTitle(..., Revision::READ_NORMAL)

The fallback to master makes sense in Revision::newFromId(), since a
revision ID known to exist by some other means might be present in the
master but not in the slave. But it doesn't make sense for
Revision::newFromTitle(), where by far the most common cause of this
case being hit is the page being nonexistent.

Change-Id: I41189fcde1b8065ac134982241376d63b78732a1