testReaction fails on ppc64

[giallu]

Possibly related to #1671, test fails like this:
[11:49:50] Testing old pickle file with new agent version
terminate called after throwing an instance of 'RDKit::MolPicklerException'
what(): std::exception

This is the bt leading to the exception:

(gdb) bt
#0  0x00003fffb74a0738 in .raise () from /lib64/power8/libc.so.6
#1  0x00003fffb74a2e54 in .abort () from /lib64/power8/libc.so.6
#2  0x00003fffb7890d04 in .__gnu_cxx::__verbose_terminate_handler() () from /lib64/libstdc++.so.6
#3  0x00003fffb788d624 in ?? () from /lib64/libstdc++.so.6
#4  0x00003fffb788d6c8 in .std::terminate() () from /lib64/libstdc++.so.6
#5  0x00003fffb788daec in .__cxa_throw () from /lib64/libstdc++.so.6
#6  0x00003fffb7b38378 in RDKit::(anonymous namespace)::buildBaseQuery<RDKit::Atom> (version=7020, tag=<optimized out>, owner=0x1001e8070, 
    ss=..., this=<optimized out>, this=<optimized out>, this=<optimized out>, this=<optimized out>, this=<optimized out>, 
    this=<optimized out>, this=<optimized out>, this=<optimized out>, this=<optimized out>)
    at /home/fedora/giallu/rdkit/Code/GraphMol/MolPickler.cpp:430
#7  RDKit::(anonymous namespace)::unpickleQuery (ss=..., owner=owner@entry=0x1001e8070, version=version@entry=7020)
    at /home/fedora/giallu/rdkit/Code/GraphMol/MolPickler.cpp:476
#8  0x00003fffb7b397bc in RDKit::MolPickler::_addAtomFromPickle<unsigned char> (ss=..., mol=0x1001edca0, pos=..., version=<optimized out>, 
    directMap=<optimized out>) at /home/fedora/giallu/rdkit/Code/GraphMol/MolPickler.cpp:1373
#9  0x00003fffb7b3676c in RDKit::MolPickler::_depickle<unsigned char> (ss=..., mol=0x1001edca0, version=<optimized out>, 
    numAtoms=<optimized out>) at /home/fedora/giallu/rdkit/Code/GraphMol/MolPickler.cpp:926
#10 0x00003fffb7b29ea4 in RDKit::MolPickler::molFromPickle (ss=..., mol=<optimized out>)
    at /home/fedora/giallu/rdkit/Code/GraphMol/MolPickler.cpp:771
#11 0x00003fffb7ede7cc in RDKit::ReactionPickler::_depickle (ss=..., rxn=0x1001e8970, version=<optimized out>)
    at /home/fedora/giallu/rdkit/Code/GraphMol/ChemReactions/ReactionPickler.cpp:185
#12 0x00003fffb7edfab8 in RDKit::ReactionPickler::reactionFromPickle (ss=..., rxn=0x1001e8970)
    at /home/fedora/giallu/rdkit/Code/GraphMol/ChemReactions/ReactionPickler.cpp:98
#13 0x0000000100024e3c in test56TestOldPickleVersion () at /home/fedora/giallu/rdkit/Code/GraphMol/ChemReactions/testReaction.cpp:5454
#14 0x0000000100010cd0 in main () at /home/fedora/giallu/rdkit/Code/GraphMol/ChemReactions/testReaction.cpp:6613