rebase: improve error messages about dirty state
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 <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>