title: beforeShowDay call a day twice
body: <p>how can i prevent that the function beforeShowDay called a day to times? The jquery datepicker has two months.</p>
  
  <pre><code>30.01.2013 -&gt; month side jan
  31.01.2013 -&gt; month side jan
  01.02.2013 -&gt; month side jan (last invisible day / placehoder)
  02.02.2013 -&gt; month side jan (last invisible day / placehoder)
  03.02.2013 -&gt; month side jan (last invisible day / placehoder)
  ----------------------------    
  28.01.2013 -&gt; month side feb (first invisible day / placehoder)
  29.01.2013 -&gt; month side feb (first invisible day / placehoder)
  30.01.2013 -&gt; month side feb (first invisible day / placehoder)
  31.01.2013 -&gt; month side feb (first invisible day / placehoder)
  01.02.2013 -&gt; month side feb
  01.02.2013 -&gt; month side feb
  02.02.2013 -&gt; month side feb
  02.02.2013 -&gt; month side feb
  03.02.2013 -&gt; month side feb
  03.02.2013 -&gt; month side feb
  04.02.2013 -&gt; month side feb
  04.02.2013 -&gt; month side feb
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/N2KhH.jpg" alt="Picture Example"></p>
  
  <p>with beforeShowDay i count days and if some days called twice, the result is not right... how can i prevent the double calls of days?</p>
  
  <p>Greetings!</p>