Bug#1053700: xarray test failure on s390x

[Rebecca N. Palmer]

This fix worked but the new upstream version added another similar 
issue, so s390x failed again.

I have pushed a fix for this, and enabled allow-stderr to fix armel 
(error output from an already-xfailed test).  I don't know what's 
causing the hang on arm64, so please do _not_ upload this just yet.