f_fastlocals in a traceback object (this is a core dump hazard
  if there are <nil> entries), but instead eval_code() merges the fast
  locals back into the locals dictionary if it looks like the local
  variables will be retained.  Also, the merge routines save
  exceptions since this is sometimes needed (alas!).

* Added id() to bltinmodule.c, which returns an object's address
  (identity).  Useful to walk arbitrary data structures containing
  cycles.

* Added compile() to bltinmodule.c and compile_string() to
  pythonrun.[ch]: support to exec/eval arbitrary code objects.  The
  code that defaults globals and locals is moved from run_node in
  pythonrun.c (which is now identical to eval_node) to eval_code in
  ceval.c.  [XXX For elegance a clean-up session is necessary.]