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.

ldo.c

@@ -372,7 +372,7 @@ void luaD_tryfuncTM (lua_State *L, StkId func) {
   const TValue *tm = luaT_gettmbyobj(L, s2v(func), TM_CALL);
   StkId p;
   if (unlikely(ttisnil(tm)))
-    luaG_typeerror(L, s2v(func), "call");  /* nothing to call */
+    luaG_callerror(L, s2v(func));  /* nothing to call */
   for (p = L->top; p > func; p--)  /* open space for metamethod */
     setobjs2s(L, p, p-1);
   L->top++;  /* stack space pre-allocated by the caller */