RFR: 203: git-pr: add flag --jcheck to run jcheck as part of git-pr create

[Erik Helin]

Hi all,

please review this patch that adds the flag `--jcheck` to `git-pr create`. As
the name suggests, adding the flag `--jcheck` to `git-pr create` will cause
`git-pr create` to run jcheck on the commits that will be part of the pull
request. Since not all messages are relevant for commits that are to be part of
a pull request (i.e. commit message errors do not matter) I added a new flag to
jcheck `--pull-request` to filter out those.

I also had to some slight refactoring to `GitJCheck.java` to allow it to be
called from other Java code.

Thanks,
Erik

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Commits:
 - becc2d9f: skara-203

Changes: https://git.openjdk.java.net/skara/pull/330/files
 Webrev: https://webrevs.openjdk.java.net/skara/330/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-203
  Stats: 42 lines in 4 files changed: 27 ins; 0 del; 15 mod
  Patch: https://git.openjdk.java.net/skara/pull/330.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/330/head:pull/330

PR: https://git.openjdk.java.net/skara/pull/330