Faster compilation speed

[Jamie Lokier]

Timothy J. Wood wrote:
>    I'm not sure what you mean.  The external RC table only gets modified 
> once every 2^N operations already (and never if the internal RC never 
> overflows the internal RC).  Stated another way, the internal RC holds 
> the low order bits and the external RC holds the high order bits.

Ah, right, I misunderstood the code.  Your way is a fine way.
Presumably if it only gets called every 2^N operations at most, then
it's not _strictly_ the high order bits in the hash table.  I.e. I'm
thinking of the reference pattern 127 -> 128 -> 127 -> 128...

-- Jamie