Bug#698240: build-rdeps also fails with lz4'd sources

[solo-debianbugs at goeswhere.com]

Control: severity -1 important

build-rdeps also fails with lz4'd sources, which appears to have become
the default in sid at some point? It's the case in the "official"
debian:sid Docker images, without any config I can see set.

As the tool is broken on a default install, without me having changed
any configuration, this bug is Important.

Chris.