title: NSDecimalNumber round long numbers
body: <p>I'm trying to get NSDecimalNumber to print out large numbers, 15 or more digits.  At 15 digits I see 111,111,111,111,111.  Above 15 digits I see 1,111,111,111,111,110 even though the number being formatted is 1111111111111111.</p>
  
  <p>An example to illustrate my problem:</p>
  
  <pre><code>NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
  [formatter setNumberStyle:NSNumberFormatterDecimalStyle];
  [formatter setMaximumSignificantDigits:25];
  [formatter setUsesSignificantDigits:true];
  
  NSDecimalNumber* test = [NSDecimalNumber decimalNumberWithString:@"12345678901234567890"];
  
  NSString* output = [formatter stringFromNumber:test]; 
  NSLog( @"num value: %@", test ); 
  NSLog( @"str value: %@", output );
  </code></pre>
  
  <p>And the output looks like:</p>
  
  <pre><code>2010-09-16 09:24:16.783 SimpleCalc[739:207] num value: 12345678901234567890
  2010-09-16 09:24:16.784 SimpleCalc[739:207] str value: 12,345,678,901,234,600,000
  </code></pre>
  
  <p>What silly thing have I missed?</p>