Let the debugger continue to the normal handler.

Let the debugger continue to the normal handler.
* src/eval.c (maybe_call_debugger): Declare before new use.
(find_handler_clause): Don't call debugger any more.
Ignore Vstack_trace_on_error.
Use XCAR/XCDR.
(syms_of_eval): Remove Vstack_trace_on_error.
(Fsignal): Only modify handlerlist when we know we need to do it.
Call the debugger when necessary.
* src/globals.h (Vstack_trace_on_error): Remove.