RFR: Age cycle periodically [v2]

[Kelvin Nilsen]

> Add option to allow object ages to increment periodically instead of on every young cycle.

Kelvin Nilsen has updated the pull request incrementally with one additional commit since the last revision:

  Cosmetic cleanup

-------------

Changes:
  - all: https://git.openjdk.java.net/shenandoah/pull/80/files
  - new: https://git.openjdk.java.net/shenandoah/pull/80/files/a679866b..5fda5a3b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=shenandoah&pr=80&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=shenandoah&pr=80&range=00-01

  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/shenandoah/pull/80.diff
  Fetch: git fetch https://git.openjdk.java.net/shenandoah pull/80/head:pull/80

PR: https://git.openjdk.java.net/shenandoah/pull/80