RFR: JDK-8272984: javadoc support for SOURCE_DATE_EPOCH

[Jonathan Gibbons]

Please review a relatively simple patch to support the standard SOURCE_DATE_EPOCH environment variable, used by those who are interested in reproducible builds. (See https://reproducible-builds.org)

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Commit messages:
 - JDK-8272984: javadoc support for SOURCE_DATE_EPOCH

Changes: https://git.openjdk.java.net/jdk/pull/6905/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6905&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8272984
  Stats: 132 lines in 5 files changed: 128 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6905.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6905/head:pull/6905

PR: https://git.openjdk.java.net/jdk/pull/6905