title: Can not find rMatClust parent point attribute
body: <p>Calling <code>rMatClust()</code> with parameter <code>saveparents=TRUE</code> is not providing with the parent point pattern in the result. How to retrieve the parent points?</p>
  <p>I am trying something like the following:</p>
  <p><code>parent.kappa &lt;- function(x,y){ exp(-8.944711 - 4.645625*10^(-5)*x -6.437164*10^(-4)*y)</code></p>
  <p><code>simulated.ppp &lt;- rMatClust(kappa=parent.kappa, scale=10, mu=5, nsim = 1, win=owin(c(0, 1000), c(0, 1000)), saveLambda=TRUE, saveparents=TRUE)</code></p>
  <p>According to the manual <code>simulated.ppp</code> should have an attribute named <code>parents</code> (a point pattern object) that holds the parent points of the Matern clusters.</p>