Delay output of sets and adds until real loops.

If the BE is using optimised tokens it's safe to delay set and adds until
the cell itself is needed or a loop starts. Without BE optimisations the
loop is recreated so a set or add may be moved into the loop with bad
effects. Print and input are safe from this but are unlikely to produce
optimal code if the BE isn't using optimised tokens.
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Add another BF doubler and other small changes
Make the DynASM jit runner faster.