RFR: Enable remembered set verification during global collections [v4]

[William Kemper]

> There are two sets of changes here:
>  * Fixes to the verifier itself to enable remembered set verification during global collection
>  * Fixes to prevent the remembered set scan from parsing unmarked objects after a global collection
> 
> These changes pass the dacapo suite with `-XX:+ShenandoahVerify` and pass the shenandoah tier1 tests.

William Kemper has updated the pull request incrementally with one additional commit since the last revision:

  Fix typo in comment

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Changes:
  - all: https://git.openjdk.java.net/shenandoah/pull/64/files
  - new: https://git.openjdk.java.net/shenandoah/pull/64/files/7136de8c..6e8b7922

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=shenandoah&pr=64&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=shenandoah&pr=64&range=02-03

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/shenandoah/pull/64.diff
  Fetch: git fetch https://git.openjdk.java.net/shenandoah pull/64/head:pull/64

PR: https://git.openjdk.java.net/shenandoah/pull/64