RFR: 8079408: Reimplement TraceClassLoading, TraceClassUnloading, and TraceClassLoaderData with Unified Logging.

[Max Ockner]

Hello,
Please review this unified logging conversion for several related flags 
in the class loading system.

Bugs:
https://bugs.openjdk.java.net/browse/JDK-8079408 (classload, 
classloaderdata)
https://bugs.openjdk.java.net/browse/JDK-8142506 (classunload)

Webrev: http://cr.openjdk.java.net/~mockner/classload.01/

Summary:

There are two separate issues here. Originally Ioi and I began working 
on these fixes in parallel, but eventually it became obvious that the 
classload and classunload tags needed to be implemented together. This 
change is a combination of Ioi's change for 8079408 and my change for 
8142506.

(1) "-XX:+TraceClassLoading" ==> "-Xlog:classload=info"
This flag is added to the alias table. More verbose logging exists at 
level debug (one level of verbosity up from info)

(2) "-XX:+TraceClassUnLoading" ==> "-Xlog:classunload=info"
This flag is added to the alias table. More verbose logging exists at 
level trace (converted from uses of WizardMode)

(3) "-XX:+TraceClassLoaderData" ==> "-Xlog:classloaderdata=debug"

The changes to TraceClassLoading and TraceClassUnloading also effected 
the implementation of "-verbose:class"

Tested with: jtreg runtime, runThese with "-Xlog:classload=trace 
-Xlog:classunload=trace -Xlog:classloaderdata=trace".

If you have questions about the updates to the classloading log, Ioi can 
give a better answer than I can.

Thanks,
Max