* Fix#3982, missing output which lacks newlines
If the last line printed to stdout or stderr was missing a
terminating newline, it would go entirely missing (in all languages).
The reason for this is a bug in the engine's handling of plugin
outputs: Go's Reader.ReadString('\n') returns a string containing what
was read and/or an error; if the string terminated in a '\n', the
error is nil, and the entire line is returned; if the stream ends,
however, a non-nil error is returned *and* what was read is returned,
even though it wasn't terminated in a newline. The fix is simple:
instead of ignoring that text, we use it, and *then* exit the read-loop.
Also added some test cases since this is subtle and easy to regress.
* Add a changelog entry