abort: added support for rebase This adds support of `rebase` to `hg abort` plan. An independent abort logic for `rebase` is created under `abortrebase()` 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`. Results of tests are shown. Differential Revision: https://phab.mercurial-scm.org/D6568