This patch makes the guile representation of lisp booleans match what
I outlined in my post of Aug 2009, "The cube of lisp booleans" [1].
The only difference from my earlier patch is the addition of two more
do-not-use IFLAGS (6 and 7), which enable more efficient
implementations of several operations.

I confess that I haven't yet tested this patch, but it's so trivial
that it must work *grin*.  Sorry, my development machine is an XO-1,
so compiling guile takes a very long time :(

     Mark

[1] http://lists.gnu.org/archive/html/guile-devel/2009-08/msg00206.html