RFR: Global mark is not old mark

[William Kemper]

Starting a global mark does not need to set old mark as in-progress and just confuses things.

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Commit messages:
 - Global mark should not manage state of old mark
 - Merge upstream into shenandoah
 - Revert "Mutator may fail to evacuate"

Changes: https://git.openjdk.java.net/shenandoah/pull/125/files
 Webrev: https://webrevs.openjdk.java.net/?repo=shenandoah&pr=125&range=00
  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.java.net/shenandoah/pull/125.diff
  Fetch: git fetch https://git.openjdk.java.net/shenandoah pull/125/head:pull/125

PR: https://git.openjdk.java.net/shenandoah/pull/125