RFR 6656031: SA: jmap -permstat number of classes is off by 1

[Jaroslav Bachorik]

Please, review the following fix.

Issue : https://bugs.openjdk.java.net/browse/JDK-6656031
Webrev: http://cr.openjdk.java.net/~jbachorik/6656031/webrev.00
The issue is caused by using SystemDictionary.ClassAndLoaderVisitor to 
traverse the dictionary classes to get the numbers of the loaded classes 
per classloader. This visitor will visit all the combinations of a 
particular class and all its classloaders - the defining CL + all 
initiating CLs. This will cause completely wrong numbers to be reported.

The solution is to use SystemDictionary.ClassVisitor which walks only 
over the loaded classes (each class exactly once) and extract the 
defining CL from the visited Klass.

Thanks,

-JB-