Request for review - 7199349

[Jon Masamitsu]

7199349: NPG: PS: Crash seen in jprt

The error is caused by the calculation in scavenge_contents_parallel()
of start_card and end_card where end_card was incorrectly set beyond
start_card.  The incorrect code had been introduced to fix a problem
exposed when the card table for perm gen was removed.  That first
problem was an assertion error resulting when byte_for() was passed
an addressed not covered by the card table.   I reverted to
the previous code and do not invoke this code when the old gen
is empty.  scavenge_contents_parallel() processes the card table
to find old-to-young pointers and so is not needed in that case.

Added a delay in two places in the young collection to widen the
opportunity for these circumstances to occur.

http://cr.openjdk.java.net/~jmasa/7199349

Thanks to StefanK for his analysis of the problem.