title: Python cx_oracle ignores numbers by positional bind variables
body: <pre><code>cursor.execute("SELECT * FROM t WHERE c1=:2 AND c2=:1", (1, 2))
  </code></pre>
  
  <p>is executed as</p>
  
  <pre><code>SELECT * FROM t WHERE c1=1 AND c2=2
  </code></pre>
  
  <p>instead of </p>
  
  <pre><code>SELECT * FROM t WHERE c1=2 AND c2=1
  </code></pre>
  
  <p>as I expected. Why?</p>
  
  <p>In fact all the :numbers are completely ignored</p>
  
  <pre><code>sql = ":5, :0, :0, :2, :1, :3"
  </code></pre>
  
  <p>is interpreted the same as</p>
  
  <pre><code>sql = ":1, :2, :3, :4, :5, :6"
  </code></pre>
  
  <p>Is this by intention or a bug?</p>