RFR: 8280832: Update usage docs for NonblockingQueue [v2]

[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 incrementally with one additional commit since the last revision:

  walulyai review

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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/8c6593dc..fe7cc130

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7393&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7393&range=00-01

  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 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