RFR: 190: git-pr: add flag --ignore-workspace

[Erik Helin]

Hi all,

please review this small patch that adds the flag `--ignore-workspace` to
`git-pr create` (also configurable). When `--ignore-workspace` is set, then
`git-pr create` won't complain if there are changes in the worktree or in the
staging area.

Thanks,
Erik

- [x] Manual testing of `git-pr create` with changes in worktree and staging area

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Commits:
 - 232e1960: skara-190

Changes: https://git.openjdk.java.net/skara/pull/316/files
 Webrev: https://webrevs.openjdk.java.net/skara/316/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-190
  Stats: 55 lines in 1 file changed: 33 ins; 22 del; 0 mod
  Patch: https://git.openjdk.java.net/skara/pull/316.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/316/head:pull/316

PR: https://git.openjdk.java.net/skara/pull/316