- generalise the per-module initialisation stubs so that we use it
  in normal (non-profiled) code too.  The initialisation stubs are
  now called '__init_<module>' rather than '_reg<module>'.

- Register foreign exported functions as stable pointers in the
  initialisation code for the module.  This fixes the foreign export
  problems reported by several people.

- remove the concept of "module groups" from the profiling subsystem.

- change the profiling semantics slightly; it should be unnecessary
  to use '-caf-all' to get reasonable profiles now.