* Make each test file runnable using `module+'.
* Make the space tests not print anything (unless they fail, of course).
* Make the `first-class?' case even "more first class" by defining their
and/or as functions. (Doesn't make a real difference for this test,
but nice to test more of the language.)
* A long-standing bug, which happened with
(let ([x (lazy (delay 1))]) (force x) (force x))
not being properly handled.
* Added `delay/strict', mostly for the below.
* Made srfi/45 reprovide it as `eager'.
* Also restricted the exports from srfi/45 to its interface.
All of these issues were reported by Andreas Rottmann.
