Clean up date formatting per bug 14067, remove assumptions that things like

Clean up date formatting per bug 14067, remove assumptions that things like
20051300000000 will work. It's fine for dates-as-integers, but goes horribly
wrong when fed to $dbr->timestamp(), which calls gmmktime(). The latter function
has a bug/feature causing any 0s in the month or day field to cause a month
or day's *subtraction*. We might want to modify timestamp() to handle that, as
I can imagine any MW code would want to rely on such a feature, but that's not
this patch.

Also set a limit for Y2K38 problems, as gmmktime() doesn't like that very much either.