title: arrayfire python free device memory
body: <p>I am tryin to use arrayfire with python.</p>
  
  <p>I have an GTX550Ti and use opencl backend since I don't seem to get cuda working (don't know if compute version 2.1 of the 550Ti is too low for arrayfire).
  I try to free memory / arrays that are allocated using statement such as</p>
  
  <pre><code>import numpy as np
  import arrayfire as af
  
  arr_h = np.arange(2**15,dtype=np.complex64)
  arr_d = af.np_to_af_array(arr_h)
  
  af.free_device(arr_d)
  </code></pre>
  
  <p>the free_device complains and says it need a pointer.
  If I use either</p>
  
  <pre><code>af.free_device(arr_d.raw_ptr())
  </code></pre>
  
  <p>or</p>
  
  <pre><code>af.free_device(arr_d.device_ptr())
  </code></pre>
  
  <p>I get an error:</p>
  
  <blockquote>
    <p>OSError: exception: access violation reading 0xFFFFFFFFFFFFFFFFFFF</p>
  </blockquote>
  
  <p>So.. what is the correct way to free memory?</p>