Request for review(S): 6817419 G1: Enable extensive verification for humongous regions

[Igor Veresov]

Enabled full verification for humongous regions. Also made sure that the 
VerifyAfterGC works with deferred updates and G1HRRSFlushLogBuffersOnVerify.
Removed unnecessary checks for a survivor regions introduced in my deferred 
updates push (is_young() is sufficient).

Also disabled initiation of the traversal-base rset construction after a full 
gc, because it's unnecessary after Andrey's fix to rebuild the rsets during 
the gc pause in parallel.

Webrev: http://cr.openjdk.java.net/~iveresov/6817419/webrev.00/

Testing: a set of nsk tests that have humongous regions and GC test suite with 
verification.

igor