find symbols in proper scope when debugging (bug #40397) * lex.h (lexical_feedback::symbol_table_context::init_scope): Delete member variable and all uses. (lexical_feedback::symbol_table_context::pop): Assert that the context is not empty before popping. (lexical_feedback::symbol_table_context::push): Use default argument. (lexical_feedback::symbol_table_context::curr_scope): If empty, return symbol_table::current_scope, not the initial scope in effect when the object is created. * oct-parse.in.yy (octave_base_parser::make_anon_fcn_handle, octave_base_parser::recover_from_parsing_function): Don't check for empty lexer.symtab_context here.

## The `oregonator'.
##
## Reference:
##
##   Oscillations in chemical systems.  IV.  Limit cycle behavior in a
##   model of a real chemical reaction. Richard J. Field and Richard
##   M. Noyes, The Journal of Chemical Physics, Volume 60 Number 5,
##   March 1974.

function dx = oregonator (x, t)

  dx = zeros (3, 1);

  dx(1) = 77.27*(x(2) - x(1)*x(2) + x(1) - 8.375e-06*x(1)^2);
  dx(2) = (x(3) - x(1)*x(2) - x(2)) / 77.27;
  dx(3) = 0.161*(x(1) - x(3));

end