RFR: Record cycle start/end in Traversal GC to avoid continuous periodic GC

[Roman Kennke]

Turns out Traversal is running into continuous back-to-back (periodic) GC
because we're never actually recording cycle start/end :-) This patch fixes
it. Gives a good boost to apps running with Traversal GC. Easily passes by
adaptive heuristic now.

http://cr.openjdk.java.net/~rkennke/traversal-record-cycles/webrev.00/

Ok?

Roman