Third times a charm.

Rebased this against master, in particular to make it compatible with
the recent block_symbol additions.  I don't have a GCC-4.1 compiler at
hand, but I don't think I'm doing anything that may trigger build
warnings.  Pierre, maybe you want to confirm?

I've also gotten round to completing the d-exp expression parser
rewrite - or at least to a nice stable point.  Will be submitting that
in patch #2.

Regards
Iain

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