Instability in Hydra build

[Rik]

4/7/16

All,

The Hydra build seems to have been flipping back and forth between success
and failure somewhat randomly.  The failure is always a segfault during
'make check' in oct-parse.in.yy-tst.  Usually there isn't much information,
but one of the runs caught this

  libinterp/parse-tree/oct-parse.in.yy-tst ....................terminate
called after throwing an instance of 'std::length_error'
  what():  basic_string::_S_create
panic: Aborted -- stopping myself...
attempting to save variables to 'octave-workspace'...
save to 'octave-workspace' complete

The failures seem to have become more consistent lately
(https://hydra.nixos.org/jobset/gnu/octave-default/all?page=1).  One thing
of note is that they all occur on i686 (32-bit) versus the x86_64
platform.  Any ideas?  Do we need to try and backout csets like gnulib::pipe?

--Rik