title: What happened between March 28th and March 29th, 1976 with the java.util.GregorianCalendar?
body: <p>Trying to use the GregorianCalendar, I got stuck on a singularity while computing the number of days since a particular date.
  In the scala interpreter, I entered :</p>
  
  <pre><code>scala&gt;import java.util.GregorianCalendar
  scala&gt;import java.util.Calendar
  scala&gt;val dateToday = new GregorianCalendar(2012,Calendar.MAY,22).getTimeInMillis()
  dateToday: Long = 1337637600000
  scala&gt;val days1 = (dateToday - (new GregorianCalendar(1976,Calendar.MARCH,28).getTimeInMillis())) / (1000*3600*24)
  days1: Long = 13203
  scala&gt;val days2 = (dateToday - (new GregorianCalendar(1976,Calendar.MARCH,29).getTimeInMillis())) / (1000*3600*24)
  days2: Long = 13203
  </code></pre>
  
  <p>I don't know if the fact that 1976 is a leap year matters, but days1 and days2 should have been separated by 1. This is the only moment in history since 1970 that this singularity happens.</p>
  
  <p>Wanting to know what is going on, I compute the difference between the two dates previously mentionned, and it gives me only exactly 23 hours of difference ! What happened on that date ? Wikipedia apparently says nothing about it.</p>
  
  <p>And even more important, how to compute the real number of days since a particular date ?</p>