stable branch does not boot: aufs not available
Since Sep 25 most test suite scenarios fail on the stable branch with "aufs not available".
Next steps: check the build log to see if
aufs.ko was correctly built, try to reproduce locally.
This matters in case we have to release a 3.16.1 emergency release before 4.0.
Upgrade Linux to 4.19.0-6, currently at 4.19.67+2+deb10u1 (refs: #17103)
Building aufs.ko against mismatched version of linux-source-4.19 and
linux-headers-4.19.0-5-* makes it unusable with linux-image-4.19.0-5-amd64.