improvements to stack traces

* @panic generates an error return trace
 * printing an error return trace no longer interferes with
   normal stack traces.
 * instead of ignore_frame_count, we look at the return address
   when you call panic, and that's the first stack trace function
   makes stack traces much cleaner - the error return trace
   flows gracefully into the stack trace
60b2031831Andrew Kelley committed on 3/10/2018, 6:38:40 AMparent20011a7
3 files changedLine totals unavailable