CRR: 6882730: G1: parallel heap verification messes up region dump

[Tony Printezis]

The webrev is here:

http://cr.openjdk.java.net/~tonyp/6882730/webrev.0/

In the fix, I just propagate the fact that heap verification failed all 
the way to the top-level ::verify call and dump the heap there, where it 
is guaranteed to be single-threaded. I also added a couple of cosmetic 
changes to the heap dump.

Tony

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| Tony Printezis, Staff Engineer   | Sun Microsystems Inc.          |
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