Don't crash if there's a modify/delete conflict on a binary file #1301
Description
Repo.modify_delete manipulates text, and thus assumes the files being modify/delete-ed are textual in nature (and more so UTF-8).
This is a problem when they're not, as the forward porting now crashes with a UnicodeDecodeError.
In that case,
- we should forward port without injecting conflict markers
- ideally we should add some sort of dedicated ping / comment to remind people that a fine was delete/modify-ed?