Backport fix from sudo 1.8.22 to fix "stair-stepped output" bug

[Simon Arlott]

sudo 1.8.20 introduced a bug in commit
44dc15d02dc0b34bf03bc971ba08d3a761c3a031
that is fixed by sudo 1.8.22 in commit
3b88cdfcd8d1a39eabbb5b7d0c8fe8f035d7a264

When the "use_pty" option is enabled, "stair-stepped output" occurs if sudo is piped to another command.

Example output attached in a text file.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: sudo 1.8.21p2-3ubuntu1.2
Uname: Linux 5.4.50+ x86_64
ApportVersion: 2.20.9-0ubuntu7.16
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Sun Aug 16 12:29:23 2020
InstallationDate: Installed on 2014-05-10 (2290 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140417)
SourcePackage: sudo
UpgradeStatus: Upgraded to bionic on 2018-11-24 (630 days ago)
modified.conffile..etc.pam.d.sudo: [inaccessible: [Errno 13] Permission denied: '/etc/pam.d/sudo']
modified.conffile..etc.sudoers: [inaccessible: [Errno 13] Permission denied: '/etc/sudoers']
modified.conffile..etc.sudoers.d.README: [inaccessible: [Errno 13] Permission denied: '/etc/sudoers.d/README']

[Simon Arlott (sa.me.uk)]

commit 3b88cdfcd8d1a39eabbb5b7d0c8fe8f035d7a264 (refs/bisect/fixed)
Author: Todd C. Miller <email address hidden>
Date: Tue Sep 26 14:21:11 2017 -0600

    Fix stair-stepped output when the output of a sudo command is piped
    to another command and use_pty is set.

[Benjamin Drung (bdrung)]

Can you provide a test case do demonstrate this behavior (and for using in https://wiki.ubuntu.com/StableReleaseUpdates)?

[Simon Arlott (sa.me.uk)]

The test case is already in the "Example output" file.

https://launchpadlibrarian.net/493705832/sudo-broken.txt