RFR (S): 8227442: Make young_index_in_cset zero-based

[Thomas Schatzl]

Hi all,

   can I have reviews for this refactoring that changes the minimum 
index for the young indices (used for determining survivors per young 
region) from -1 to 0?

This avoids some imho unnecessary increment in the 
copy_to_survivor_space() method.

CR:
https://bugs.openjdk.java.net/browse/JDK-8227442
Webrev:
http://cr.openjdk.java.net/~tschatzl/8227442/webrev/
Testing:
hs-tier1-5 almost done with no issues

Thanks,
   Thomas