begin removal of global error_state variable * gripes.h, gripes.cc (gripe_library_execution_error): Delete. * error.cc (warning_state): Delete unused variable. (reset_error_handler): Don't set warning_state or error_state. (debug_or_throw_exception): New static function. (verror): Don't check error_state. (vmessage): Call debug_or_throw_exception instead of setting error_state. (error_1, error_2): Combine into single function, error_1 that prints error message and ultimately calls debug_or_throw_exception. (verror, verror_with_cfn, verror_with_id_cfn): Call error_1. Don't check or set warning_state. (error): Don't check error_state. (Flasterror, Flasterr): Adapt to not using error_state. (interpreter_try): Don't unwind_protect error_state. * NEWS: Update. * doc/interpreter/external.txi: Explain octave_execution_exception instead of error_state for matrix addition example. * jit-typeinfo.cc (octave_jit_gripe_nan_to_logical_conversion, octave_jit_ginvalid_index, octave_jit_gindex_range, octave_jit_paren_scalar, octave_jit_paren_scalar_subsasgn): Don't catch octave_execution_exception. * cellfun.cc (Fcellfun): Use exceptions instead of error_state. * ls-mat-ascii.cc (save_mat_ascii_data): Likewise. * mex.cc (mexCallMATLAB, mexEvalString): Likewise. * variables.cc (safe_symbol_lookup): Likewise. * svd.cc (Fsvd): Eliminate use of error_state. * __magick_read__.cc (read_file, write_file): Likewise. * variables.cc (generate_struct_completions): Eliminate use of obsolete warning_state variable. * ov-builtin.cc (octave_builtin::do_multi_index_op): Don't catch octave_execution_exception and call gripe_library_execution_error. * ov-class.cc (octave_class::reconstruct_exemplar): Eliminate use of error_state. Catch possible octave_execution_exception in do_multi_index_op. * ov-mex-fcn.cc (octave_mex_function::do_multi_index_op): Eliminate use of error_state. Catch possible octave_execution_exception in call_mex. * ov-fcn-handle.cc (octave_fcn_binder::maybe_binder): Eliminate use of error_state. * ov-oncleanup.cc (octave_oncleanup::~octave_oncleanup): Eliminate use of error_state. Propagate possible octave_execution_exception from do_multi_index_op. * ov.cc (octave_value::assign, do_binary_op, do_unary_op, octave_value::do_non_const_unary_op): Don't catch octave_execution_exception here. * oct-parse.in.yy (octave_base_parser::finish_colon_expression, octave_base_parser::finish_array_list): Eliminate use of warning_state and error_state. (Feval, Fevalin): Use exceptions instead of error_state. * pt-eval.cc, pt-eval.h (tree_evaluator::unwind_protect_exception): New static variable. * (tree_evaluator::visit_statement): Don't catch octave_execution_exception here. (tree_evaluator::visit_try_catch_command, tree_evaluator::do_unwind_protect_cleanup): Eliminate use of error_state. (tree_evaluator::visit_unwind_protect_command): Use unwind_protect_exception to track whether an exception has occurred in the try block.