stlfilt: read ugly tmpl errors

There's nothing better for Monday mornings than the smell of hundreds of template errors after a make clean all. When using template metaprogramming, a tiny misplaced coma can generate enough error code that, if printed, would crush you under tones of paper. And don't even try to read them, it'll make your head explode.

Luckily STLFilt can be quite a relief when dealing with this kind of errors. Granted, it won't make a steaming pile of poo seem to be a nice poem, but if you have something like the dog in the picture, to use a metaphor, at least it would put a blanket on its face.