More work on thread scheduling and tracebacks

luprex/core/cpp/traceback.hpp

@@ -15,10 +15,10 @@
 
 // traceback_coroutine
 //
-// Given a coroutine which contains an error message, pop the error
-// message from the coroutine, and push a traceback onto L.
+// Given a coroutine which contains an error message, replace
+// the error message with a full traceback.  Always returns 1.
 //
-void traceback_coroutine(lua_State *L, lua_State *CO);
+int traceback_coroutine(lua_State *L);
 
 // traceback_pcall
 //