RFR [M][7/7]: 8197932: Better split work in rebuild remembered sets phase

[Thomas Schatzl]

Hi all,

  Stefan proposed to use some iterator over the work area that
internally handles the boundary at the TAMS wrt to liveness when
scanning.

This makes the change a bit more compact, performance does not seem to
differ, so why not... :)

Webrevs:
http://cr.openjdk.java.net/~tschatzl/8197932/webrev.1_to_2/ (diff)
http://cr.openjdk.java.net/~tschatzl/8197932/webrev.2/ (full)
testing:
hs-tier1-5

Thanks,
  Thomas