fix ali httpdns bug, use no cache policy.

@@ -206,7 +206,10 @@ static float kprogressViewRadius = 2.0f;
 - (void)loadWebUrl:(NSString *)url
 {
     self.startPage = url;
-    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:url]];
+    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:url]
+                                                           cachePolicy:NSURLRequestReloadIgnoringLocalCacheData
+                                                       timeoutInterval:20];
+
     if ([self.delegate respondsToSelector:@selector(explorerWillLoadRequest:)]) {
         [self.delegate explorerWillLoadRequest:request];
     }