Fixed Field_datetime to never accept any bad datetimes as a string. This broke dozen or so test cases of course, which are riddled with 0000-00-00 00:00:00 crap.
Also, probably against my better judgment, I added the ability to match a string in the following datetime expression:
YY-MM-DD HH:mm:SS
I say against my better judgment because it looks similar to the ISO 8601:1988 standard format specifier, but is NOT since ISO always expects a 4-digit year. But, to be compatible with MySQL...