Better error messages for calling non-callable objects

When available, use the calling code to find a suitable name for what
was being called; this is particularly useful for errors of non-callable
metamethods. This commit also improved the debug information for
order metamethods.

ldebug.h

@@ -31,6 +31,7 @@ LUAI_FUNC const char *luaG_findlocal (lua_State *L, CallInfo *ci, int n,
                                                     StkId *pos);
 LUAI_FUNC l_noret luaG_typeerror (lua_State *L, const TValue *o,
                                                 const char *opname);
+LUAI_FUNC l_noret luaG_callerror (lua_State *L, const TValue *o);
 LUAI_FUNC l_noret luaG_forerror (lua_State *L, const TValue *o,
                                                const char *what);
 LUAI_FUNC l_noret luaG_concaterror (lua_State *L, const TValue *p1,