[PATCH] Teach cherry-pick and rebase to ignore redundant commits

This patch set adds a --skip-redundant-commits option to both cherry-pick and rebase. Currently, if cherry-pick applies a commit that happens to become empty after conflict resolution, it will abort and ask the user what to do. This behavior propagates to rebase when rebase is forced to fall back to cherry-pick in certain situations.

This abort failure mode makes it difficult to script certain types of operations that users might expect to work: for example cherry-picking a commit on top of itself or rebasing a set of commits back onto its own history.

With --skip-redundant commits users and/or scripts can choose to have cherry-pick/rebase simply ignore the redundant commit and move on. There is already a --keep-redundant-commits flag so this is really just supplying the natural counter-behavior users might way.

                     -Davod