[ODE] various ODE tidyups

[Russ Smith]

i've just checked in:

* various tidyups to the makefiles - now OPCODE builds from the top
  level makefile.
* fixed up the DLL defs files, now there are with- and without-OPCODE
  versions that should both work.
* use 'size_t' instead of 'int' for the allocator function arguments,
  and in various other places.
* fixed a few warnings (loss of precision, implicit cast to bool).
* removed the debugging allocator from memory.cpp, since it is very old
  and there are much better alternatives now.

russ.

-- 
Russell Smith
http://www.q12.org