Reduce CHECK_STACK, CDEBUG and RETURN stack usage (caused by GCC 2.x bug) -

Reduce CHECK_STACK, CDEBUG and RETURN stack usage (caused by GCC 2.x bug) -
  this uses __builtin_dwarf_cfa() to get stack depth on ia64 which is
  _supposed_ to be much better than __builtin_stack_frame(), but if problems
  appear on ia64 again we can just live without stack info for now.
Add optional no-op CDEBUG/ENTRY/RETURN macros (improves perf noticably).
Remove some CVS $Id tags (might be some initial merge conflicts from that,
  but saves us more in the future).