bug#61396: diff mode could distinguish changed from deleted lines

[Stefan Monnier]

>> I have been bitten several times in the past when going through largish
>> diffs where I overlooked important things in the added/removed parts
>> because they were colored the same was as the unchanged parts of
>> changed lines and so I just glossed over them.
>
> I realized now the same problem exists even without color highlighting
> at all.

No, the problem I describe is specific to the "refined" diff
highlighting: I rely on this highlighting to tell me what has "really"
been changed, yet it's not applied to lines that are "just added" or
"just removed" so I end up skipping over them unwittingly because they
are highlighted identically to the *unchanged* parts of those lines
which are otherwise changed.


        Stefan