Workaround not to use ``cdef vector[int]`` in cdef class.
Workaround not to use ``cdef vector[int]`` in cdef class.

Travis CI tests for Python 3.2 using gcc 3.7 give an error:
Cython generated C contains uninitialized references.

symengine/symengine.py,bjodah/symengine.py,bjodah/symengine.py,bjodah/symengine.py,symengine/symengine.py,symengine/symengine.py