text: Title: Error when loading multiple models - Tensor name not found
  Body: In my code, I'm loading two DNN models. Model A is a normal DNN with fully-connected layers, and Model B is a Convolutional Neural Network similar to the one used in the MNIST example. 
  
  Individually, they both work just fine - they train properly, they save properly, they load properly, and predict properly. However, when loading both neural networks, tflearn crashes with an error that seems to indicate `"Tensor name 'example_name' not found in checkpoint files..."`
  
  This error will be thrown for whatever model is loaded second (i.e. Model A will load and run correctly but Model B will not, and if the order is switched, then vice-versa). This happens even when the models are saved in and loaded from completely different directories. I'm guessing it's some sort of internal caching problem with the checkpoint files. Any solutions?
  
  Here's some more of the stack trace, if it helps
  
  ```
  File "/usr/local/lib/python2.7/site-packages/tflearn/models/dnn.py", line 227, in load
      self.trainer.restore(model_file)
    File "/usr/local/lib/python2.7/site-packages/tflearn/helpers/trainer.py", line 379, in restore
      self.restorer.restore(self.session, model_file)
    File "/usr/local/lib/python2.7/site-packages/tensorflow/python/training/saver.py", line 1105, in restore
      {self.saver_def.filename_tensor_name: save_path})
    File "/usr/local/lib/python2.7/site-packages/tensorflow/python/client/session.py", line 372, in run
      run_metadata_ptr)
    File "/usr/local/lib/python2.7/site-packages/tensorflow/python/client/session.py", line 636, in _run
      feed_dict_string, options, run_metadata)
    File "/usr/local/lib/python2.7/site-packages/tensorflow/python/client/session.py", line 708, in _do_run
      target_list, options, run_metadata)
    File "/usr/local/lib/python2.7/site-packages/tensorflow/python/client/session.py", line 728, in _do_call
      raise type(e)(node_def, op, message)
  tensorflow.python.framework.errors.NotFoundError: Tensor name "Accuracy/Mean/moving_avg_1" not found in checkpoint files classification_classifier.tfl
       [[Node: save_5/restore_slice_1 = RestoreSlice[dt=DT_FLOAT, preferred_shard=-1, _device="/job:localhost/replica:0/task:0/cpu:0"](_recv_save_5/Const_0, save_5/restore_slice_1/tensor_name, save_5/restore_slice_1/shape_and_slice)]]
  Caused by op u'save_5/restore_slice_1', defined at:
  ```
  