Git rebase conflict 'resolve using mine' doesn't work

Git and Hg treat rebase conflicts differently; Hg treats it as an unresolved merge conflict (except that parent1 is 'theirs' rather than 'mine'). In git there is only one parent during a rebase conflict, which is 'theirs', and there is no direct way to get the SHA of 'mine'.

This means that the generalised approach to Resolve Using Mine between rebase and merge is not working in the case of a git rebase conflict.

Should change the implementation to be separately implemented in each subsystem instead of just the SHA information being delegated.