Use older version of pyyaml for tests under Python 3.2
Use older version of pyyaml for tests under Python 3.2

sosy-lab/benchexec,sosy-lab/benchexec,ultimate-pa/benchexec,sosy-lab/benchexec,dbeyer/benchexec,dbeyer/benchexec,sosy-lab/benchexec,sosy-lab/benchexec,ultimate-pa/benchexec,ultimate-pa/benchexec,ultimate-pa/benchexec,dbeyer/benchexec,ultimate-pa/benchexec,sosy-lab/benchexec,dbeyer/benchexec,ultimate-pa/benchexec