request for a "defined" tester, perhaps "def"

[torbjorn]

To be used like this:

cmp_deeply(
    $foo,
    methods(
        bar => def,
        ...,
    ),
    "among other things, the bar method returns something defined"
);

[Ovid]

And an undefined version. We're been stamping out warnings in our test suite caused by expected undefined values throwing warnings when we use superbagof and I expect cmp_deeply might have the same issues.