Add indicators for interactive rebase and bisect

[compholio]

These commits add support for several nice conveniences:

• A wrench indicator for interactive rebase.
• A binoculars indicator for bisecting.
• Revision progress for bisecting (tested commits / commits remaining).
• Approximate number of remaining bisect steps.

I don't know about everyone else, but rebasing and bisecting are a critical part of my workflow and having indications for that helps me to avoid making a lot of mistakes.