RFR (M): 8129558: Coalesce dead objects during removal of self-forwarded pointers

[Thomas Schatzl]

Hi all,

  another round of the changes available at

http://cr.openjdk.java.net/~tschatzl/8129558/webrev.2 (full)
http://cr.openjdk.java.net/~tschatzl/8129558/webrev.1_to_2 (diff)

It fixes:
 - comments
 - typo in variable name
 - removes passing around the G1CollectedHeap
 - fixes the problem with the BOT of the potential second filler object
which is now updated correctly I think.

Thanks,
  Thomas