* Patch is less sensitive to the file names in the diff headers than
  the scripts are. It tries both filenames specified and apparently
  checks if the file exists. We only look at the `+++ file ...' header,
  and ignore the other. Other than patch we cannot simply look at the
  file system to determine which one is the imput file.

* Patch destroys the backup files it generates if a file appears more
  than once in a patch. This is the reason why we use the backup-files
  utility instead.