Some old (but still widely in use) versions of GNU diff have a bug where

they may at times fail to generate a \ No newline at end of file

marker for files that lack a trailing newline. Modern GNU Patch does not

work around this case, and fails with an error.
We now attempt to work around this issue. If a patch fails to apply, we

begin to investigate the diff. If it lacks a trailing newline, and we

don't see this marker anywhere in the diff, we will attempt to add a

newline and patch again.
This is not always guaranteed to work. It's a best-effort attempt at

working around a problem with how the diff is generated. We never hit it

unless we've already failed to patch, though.

Unit tests pass.