Renamed section on compactness to "Compactness of the interval"

It was mostly Steve who worried that I would put into the chapter
on reals some sort of fundamentalist constructivsm. His fears were
possibly well founded, who knows.

In any case, since the chapter on reals mentions the word "classical"
21 times (only the introduction does it more often, 21) and keeps saying
how everything is compatible with classical logic, it maybe isn't too
fundamentalist to call the chapter on compactness "Compactness".