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.
we can name this function abortrebase, no need to add hg in front.