Fix new recovery test for use under msys

Fix new recovery test for use under msys

Commit caba8f0d43 wasn't quite right for msys, as demonstrated by
several buildfarm animals, including jacana and fairywren. We need to
use the msys perl in the archive command, but call it in such a way that
Windows will understand the path. Furthermore, inside the copy script we
need to convert a Windows path to an msys path.