Fixes#223. Very simple reproduction
```
cd diffutils
mkdir a
touch a/alef a/alefn a/alef_ a/alefx a/alefr a/fuzz.file
cargo test
```
=> fail
https://www.gnu.org/software/diffutils/manual/html_node/Multiple-Patches.html
states that the "old" file name has precedence over the "new" filename.
I hit this problem because some other (and unfortunately: unknown for
now) test issue left bogus `a/alef*` file(s) behind in my workspace. I
didn't bother cleaning them up because I assumed some test would keep
recreating them and that cost me a lot of time.
This issue seems to have existed since the very first commit.
Interestingly, there as a previous attempt in 2024 to fix this in commit
a3a372ff36 ! So I was apparently not the only affected. BUT that
fix was immediately reverted by commit ba7cb0aef9 in the same
PR. Admittedly, that fix seemed somewhat off-topic in
https://github.com/uutils/diffutils/pull/33. So here it is again.
Marc Herbert
pocopepe
Olivier Tilloy
hanbings
Sylvestre Ledru
Michael Howell