For the less common conflict types DD, AU, UA, DU, and UD, we would previously
only show "* Unmerged path" in the main view, which isn't helpful. Also, for
some of these we would split the main view and show this text both in the
unstaged changes and staged changes views, which is a bit embarrassing.
Improve this by offering more explanation about what's going on, and what the
most likely way to resolve the situation is for each case.
2e1be45957