RFR: 2089: Warn when bug fixVersion doesn't match .jcheck/conf version in PR [v3]

[Zhao Song]

> This patch tries to alert the user when the fixVersion in the issue differs from the fixVersion in .jcheck/conf, thereby preventing the creation of unwanted backports.

Zhao Song has updated the pull request incrementally with one additional commit since the last revision:

  rename fixVersionOverride to versionMismatchWarning

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Changes:
  - all: https://git.openjdk.org/skara/pull/1585/files
  - new: https://git.openjdk.org/skara/pull/1585/files/9a61116e..4cdc4b2e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=skara&pr=1585&range=02
 - incr: https://webrevs.openjdk.org/?repo=skara&pr=1585&range=01-02

  Stats: 15 lines in 5 files changed: 1 ins; 1 del; 13 mod
  Patch: https://git.openjdk.org/skara/pull/1585.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1585/head:pull/1585

PR: https://git.openjdk.org/skara/pull/1585