title: AM/PM issue in NSDateFormatter
body: <p>I write below code to convert one date format into another dateformat.
  But AM string works and PM did not work .
  Please help-</p>
  
  <pre><code>dateTime=@"2013-01-24 18:30 PM";
  //dateTime=@"2013-01-24 06:30 AM";
  NSDateFormatter *dtFormatter=[[NSDateFormatter alloc]init];
  [dtFormatter setDateFormat:@"yyyy-MM-dd hh:mm a"];
  NSDate *AptDate=[dtFormatter dateFromString:dateTime];
  [dtFormatter setDateFormat:@"MMM dd,yyyy hh:mm a"];
  NSString *strDate=[dtFormatter stringFromDate:AptDate];
  </code></pre>
  
  <p>Here I get AptDate variable as null if i use PM format</p>