warning: `%y' yields only last 2 digits of year

[Robert Dewar]

<<Just consider for a moment that, after seeing the 19%y example in the
docs, the user might think that the sequence 19%y is handled
especially, and will actually print the full year.  It's amazing how
people's imaginations sometimes fly :-)
>>

But then if you imagine people being this far out to lunch, you will start
to generate all kinds of warnings about imagined incompetence :-)

For instance, unconditionally warning when a switch branch does not
end with a break, or warning that an if is missing an else part.