title: Force symmetry for a TensorFlow conv2d kernel
body: <p>I'd like to enforce symmetry in the weights within a Variable.  I really want an approximate circular symmetry.  However, I could imagine either row or column enforced symmetry.</p>
  
  <p>The goal is to reduce training time by reducing the number of free variables.  I know my problem would like a symmetric array but I might want to include both symmetric and "free" variables.  I am using conv2d now, so I believe I need to keep using it.</p>