title: Issue with ST_CONTAINS and ST_WITHIN in PostGIS
body: <p>My environment: PostgreSQL 11.4 with PostGIS 2.5.2 </p>
  
  <pre class="lang-sql prettyprint-override"><code>CREATE TABLE m_polygon (id SERIAL PRIMARY KEY, bounds POLYGON);
  INSERT INTO m_polygon(bounds) VALUES( 
    '(0.0, 0.0),  (0.0, 10.0), (10.0, 0.0), (10.0, 10.0), (0,0)' 
  );
  
  SELECT ST_WITHIN(m_polygon.bounds , m_polygon.bounds ) FROM m_polygon;
  </code></pre>
  
  <p>I am getting the error message for SELECT statement above:</p>
  
  <pre><code>ERROR:  function st_within(polygon, polygon) does not exist 
  HINT:  No function matches the given name and argument types. You might 
  need to add explicit type casts
  </code></pre>
  
  <p>I was thinking what the reason for the error is:  the ST_WITHIN arguments types should be GEOMETRY, but I am passing the POLYGONs. </p>
  
  <p>However  the following works:</p>
  
  <pre class="lang-sql prettyprint-override"><code>SELECT ST_WITHIN(ST_MakePoint(1,1), ST_MakePoint(1,1) ) ;
  </code></pre>