A coroutine can close itself

A call to close itself will close all its to-be-closed variables and
return to the resume that (re)started the coroutine.

ldo.h

@@ -91,6 +91,7 @@ LUAI_FUNC void luaD_shrinkstack (lua_State *L);
 LUAI_FUNC void luaD_inctop (lua_State *L);
 
 LUAI_FUNC l_noret luaD_throw (lua_State *L, TStatus errcode);
+LUAI_FUNC l_noret luaD_throwbaselevel (lua_State *L, TStatus errcode);
 LUAI_FUNC TStatus luaD_rawrunprotected (lua_State *L, Pfunc f, void *ud);
 
 #endif