If you have unstaged changes in your working tree and try to rebase, you will get the cryptic "foo: needs update" message, but nothing else. If you have staged changes, you get "your index is not up-to-date".
Let's improve this situation in two ways:
- for unstaged changes, let's also tell them we are canceling the rebase, and why (in addition to the "needs update" lines)
- for the staged changes case, let's use language that is a little more clear to the user: their index contains uncommitted changes
Signed-off-by: Jeff King <email@example.com> Signed-off-by: Junio C Hamano <firstname.lastname@example.org>