Please review fix to StackOverflowError in jigsaw tracing

[Mandy Chung]

I have a fix for:
   6951456: jigsaw JIGSAW_TRACE=3 stack overflow due to recursion

Trace may be called while the classes for tracing (e.g. java.util.Formatter)
are being loaded. One solution is to cache the traces to avoid recursion
until the very first call completes.

Webrev at:
   http://cr.openjdk.java.net/~mchung/6951456/webrev.00/

Thanks
Mandy