Function 'warn' is vararg

Instead of a 'tocont' flag, the function 'warn' in Lua now receives all
message pieces as multiple arguments in a single call. Besides being
simpler to use, this implementation ensures that Lua code cannot create
unfinished warnings.

lbaselib.c

@@ -37,9 +37,20 @@ static int luaB_print (lua_State *L) {
 }
 
 
+/*
+** Creates a warning with all given arguments.
+** Check first for errors; otherwise an error may interrupt
+** the composition of a warning, leaving it unfinished.
+*/
 static int luaB_warn (lua_State *L) {
-  const char *msg = luaL_checkstring(L, 1);
-  lua_warning(L, msg, lua_toboolean(L, 2));
+  int n = lua_gettop(L);  /* number of arguments */
+  int i;
+  luaL_checkstring(L, 1);  /* at least one argument */
+  for (i = 2; i <= n; i++)
+    luaL_checkstring(L, i);  /* make sure all arguments are strings */
+  for (i = 1; i <= n; i++)  /* compose warning */
+    lua_warning(L, lua_tostring(L, i), 1);
+  lua_warning(L, "", 0);  /* close warning */
   return 0;
 }