Working towards being able to pre-compile the GEL at the time the
rule is loaded, rather than doing the compiles on the fly as-needed.
That way *all* of the GEL expansions will have been populated, which
means they're providing a stable memory image that can be safely read
by multiple threads without a need for further updating of the objects
(which would require synchronized APIs if the memory image weren't
stable.)

This is step 1 towards being able to multi-thread this beastie of mine.