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

[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.

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Commit messages:
 - fix an issue
 - add test
 - SKARA-2089

Changes: https://git.openjdk.org/skara/pull/1585/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1585&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-2089
  Stats: 79 lines in 3 files changed: 76 ins; 0 del; 3 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