`split("\n")` includes a final empty element `""` if the final line
ends with `\n` (as it should for POSIX-compliant text files), which
then became an extra `"\n"`.
`splitlines()` solves that, but there's a caveat, as it will split
on other types of line breaks too (like `\r`), which may not be
desired.
Fixes#526.