std.unittests for (final?) review

[bearophile]

Andrei:

> One more thing. Since assert() is available and useful outside 
> unittests, I don't see a reason for which assertPred and friends should 
> only be available during unittesting. I can sure use them in regular code.

I guess assertPred creates statistics to be printed at the end of the unittests? I don't think mixing the two groups of things is good.

Bye,
bearophile