RFR: git-jcheck: add support for multiple pre-push hooks

[Erik Helin]

Hi all,

please review this patch that adds support for multiple kinds of pre-push hooks
to `git-jcheck`. A user can now set up either the "branches" pre-push hook
and/or the "commits" pre-push hook via `git jcheck
--setup-pre-push-hooks=commits,branches`. The "commits" pre-push hook will run
all commits about to pushed throught `git-jcheck`. The "branches"
pre-push hook will check that you are not pushing to a branch in your personal
fork that is also present in the upstream repository (rarely a good idea).

Testing:
- Manual testing of pre-push hooks and `git-jcheck` on Linux x64

Thanks,
Erik

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Commits:
 - fa996599: git-jcheck: add support for multiple pre-push hooks

Changes: https://git.openjdk.java.net/skara/pull/474/files
 Webrev: https://webrevs.openjdk.java.net/skara/474/webrev.00
  Stats: 118 lines in 3 files changed: 96 ins; 10 del; 12 mod
  Patch: https://git.openjdk.java.net/skara/pull/474.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/474/head:pull/474

PR: https://git.openjdk.java.net/skara/pull/474