that required explicitly calling LazyList.clear() in the two tests that
use LazyList (I added a LazyList Fibonacci generator too).

A real bitch:  the extremely inefficient first version of the 2-3-5 test
*looked* like a slow leak on Win98SE, but it wasn't "really":  it generated
so many results that the heap grew over 4Mb (tons of frames!  the number
of frames grows exponentially in that test).  Then Win98SE malloc() starts
fragmenting address space allocating more and more heaps, and the visible
memory use grew very slowly while the disk was thrashing like mad.
Printing fewer results (i.e., keeping the heap burden under 4Mb) made
that illusion vanish.

Looks like there's no hope for plugging the LazyList leaks automatically
short of adding frameobjects and genobjects to gc.  OTOH, they're very
easy to break by hand, and they're the only *kind* of plausibly realistic
leaks I've been able to provoke.

Dilemma.