RFR (S): 8073146: G1 merges thread local age tables too early with global age table

[Thomas Schatzl]

Hi,

  here is the mentioned fix for 8073146 which resolves a day-one issue
with age table statistics and per-region survivor statistics.

Basically G1 only ever merged the age table/region survivor statistics
at the end of the first parallel phase, forgetting any objects copied
later.

This is based on the change for 8040162 that is currently out for
review.

CR:
https://bugs.openjdk.java.net/browse/JDK-8073146
Webrev:
http://cr.openjdk.java.net/~tschatzl/8073146/webrev/
Testing:
jprt, lots of testing with various benchmarks

Thanks,
  Thomas