Current debian testing has Python 2.7.13-RC1, which has a serious
regression (upstream https://bugs.python.org/issue5322) which should be
reverted for RC2 (or the final 2.7.13).  Ignore build failures for this
build test temporarily (with the intention of reverting this commit in a
couple of weeks once it stops failing, i.e. when debian testing picks up
an updated python 2.7 release).