This adds support of `rebase` to `hg abort` plan.
An independent abort logic for `rebase` is created
under `hgabortrebase()` function. For this a seperate
`rebaseruntime` object is created under the function to
handle an unfinished `rebasestate` and abort that using
abort logic under `_prepareabortorcontinue`.
`rebase` currently supports `--dry-run` flag but not
Results of tests are shown.