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On 16.04, fix:
…/dynamic-graph-python-4.0.0/include/dynamic-graph/python/dynamic-graph-py.hh:35:25: error: 'stl_input_iterator' is not a member of 'bp'
return std::vector(bp::stl_input_iterator(iterable), bp::stl_input_iterator());
^

to fix #39 also in Python2

As PyState_AddModule is not yet called in the module definition,
PyState_FindModule will not work, so for Python 3 we need to get the
module from the methods definition to retrieve a pointer to dgpyError.

Fix #39