RFR: 8280832: Update usage docs for NonblockingQueue [v4]

[Kim Barrett]

> Please review this update of the usage and implementation comments for
> NonblockingQueue to discuss the ABA issue in push/append operations.

Kim Barrett has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - Merge branch 'master' into nbq-aba
 - dholmes review
 - walulyai review
 - document ABA for push/append

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7393/files
  - new: https://git.openjdk.java.net/jdk/pull/7393/files/7aacc083..4f03fd58

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7393&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7393&range=02-03

  Stats: 3101 lines in 57 files changed: 2579 ins; 211 del; 311 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7393.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7393/head:pull/7393

PR: https://git.openjdk.java.net/jdk/pull/7393