One of our users tried to use `hg absorb -e` but it seemed that it
would only bring up the editor if there were no changes the command
could automatically detect destination for. I spent probably half an
hour debugging why it worked that way. I finally figured out that it
does bring up the editor, but you have to answer "yes" to the "apply
changes" prompt *first*. That seems very unintuitive. If the user
wants to edit the changes, there seems to be little reason to present
them with a prompt first, so let's have `-e/--edit-lines` imply
`-a/--apply-changes`. All the tests using `-e` also already used
`-a`. I changed them to rely on the implied `-a` so we get coverage of
that.

Differential Revision: https://phab.mercurial-scm.org/D12550