Detect "Subject: [PATCH X/Y]" in patch files
git format-patch with multiple patches, it will generate subject lines like
[PATCH 1/3]. This isn't useful for aports, because once the amount of patches changes (e.g. because a patch got upstreamed), the total number is wrong and running
git format-patch for the remaining patches rebased on the new source would change the total count in all patch files. It leads to bigger diffs.
So I suggest we warn about this, and recommend using
git format-patch -N instead to omit the numbers.