guile 1.9.2

[Doug Evans <dje at sebabeach dot org>]

Guile 1.9.2 has a faster engine (based on some simple, and admittedly
too-trivial experiments), but there is hope.

I tried running cgen with it and after getting some issues out of the way (*1),
I ran into some problems that seemed internal to Guile so I'm punting for now.

mzscheme and qscheme are faster.
qscheme is simple yet fast, although gcc-specific.
I'm guessing it's also a bit incomplete for what we need, but that can change.
mzscheme is the fastest I've tried.
Some might like to develop cgen in drscheme.
Ports to any of these might be interesting.
Removing COS along the way wouldn't be a bad idea.  In time.
[Insert plans for what I'd *really* like to see happen:
a Scheme that used cgen to generate parts of its dynamic compilation backend.]

(*1) Guile 1.9.2 doesn't like top level definitions inside conditionals,
for example.  That may change (or may just be temporary) of course.