More robust value stack handling for dbg messages
More robust value stack handling for dbg messages

- Change duk__debug_process_message() to store/restore value stack top
  for message handlers.  This is more robust than requiring that every
  debug message handler code path always manages the value stack 100%
  correctly.

- Change existing message handlers so that trivial value stack cleanups
  are not done in the message handler.  Value stack popping is still
  necessary for loops where the value stack might grow without bound.

tassmjau/duktape,svaarala/duktape,jmptrader/duktape,harold-b/duktape,markand/duktape,jmptrader/duktape,harold-b/duktape,svaarala/duktape,jmptrader/duktape,tassmjau/duktape,tassmjau/duktape,harold-b/duktape,tassmjau/duktape,tassmjau/duktape,tassmjau/duktape,markand/duktape,markand/duktape,harold-b/duktape,svaarala/duktape,tassmjau/duktape,jmptrader/duktape,jmptrader/duktape,harold-b/duktape,jmptrader/duktape,svaarala/duktape,harold-b/duktape,markand/duktape,harold-b/duktape,markand/duktape,markand/duktape,harold-b/duktape,jmptrader/duktape,tassmjau/duktape,jmptrader/duktape,svaarala/duktape,harold-b/duktape,svaarala/duktape,tassmjau/duktape,harold-b/duktape,markand/duktape,jmptrader/duktape,svaarala/duktape,svaarala/duktape,jmptrader/duktape,markand/duktape,markand/duktape,markand/duktape,svaarala/duktape,tassmjau/duktape