benchmark: Update to the latest jsonpickle API
benchmark: Update to the latest jsonpickle API

jsonpickle no longer has _set_backend(), so use the provided
set_preferred_backend() function.  This also updates the benchmark
so that it is Python-2.6-friendly.

Signed-off-by: Dan Buch <daniel.buch@gmail.com>
Signed-off-by: David Aguilar <davvid@gmail.com>

git-svn-id: 93f2f39c93ae088b792869c1b97110104553f60a@63 ba5bf794-d048-0410-8f42-e1fdefefffeb

mandx/jsonpickle,mandx/jsonpickle,mandx/jsonpickle,dongguangming/jsonpickle,dongguangming/jsonpickle,dongguangming/jsonpickle,dongguangming/jsonpickle,mandx/jsonpickle,eoghanmurray/jsonpickle_prev,eoghanmurray/jsonpickle_prev