RFR: jcheck: duplicate-issues should only check id and support "dup"

[Erik Helin]

Hi all,

please review this patch that makes the "duplicate-issues" check in JCheck
_only_ consider issue ids (e.g. `8123456`) when looking for duplicates. I also
added support for the "legacy" .jcheck/conf parser to understands the `bugids =
dup` configuration line.

Testing:
- Manual testing on Linux x64

Thanks,
Erik

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Commit messages:
 - jcheck: duplicate-issues should only check id and support "dup"

Changes: https://git.openjdk.java.net/skara/pull/533/files
 Webrev: https://webrevs.openjdk.java.net/skara/533/webrev.00
  Stats: 11 lines in 2 files changed: 5 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/skara/pull/533.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/533/head:pull/533

PR: https://git.openjdk.java.net/skara/pull/533