title: AddYear method doesn't work as excpected
body: <p>I need to add years to a <code>DateTime</code> variable, but for some reason this function doesn't affect at all..</p>
  
  <p>This is my code:</p>
  
  <pre><code>DateTime dtCmp = new DateTime(calendarBirthDay.Value.Year, calendarBirthDay.Value.Month, calendarBirthDay.Value.Day);
  dtCmp.AddYears(DateTime.Now.Year - calendarBirthDay.Value.Year);
  </code></pre>
  
  <p>I tried even something trivial likewise :</p>
  
  <pre><code>dtCmp.AddYears(1);
  </code></pre>
  
  <p>and this is doesn't work yet..</p>