Adds two elements @a,@b of the same type into @result using @relicAddFunc.

def _add(a, b, relicAdd):
    """
    Adds two elements @a,@b of the same type into @result using @relicAddFunc.
    """
    # Check types, create a result object of the same type, and call the relic
    # function.
    assertSameType(a,b)
    result = type(a)()
    relicAdd(byref(result), byref(a), byref(b))
    return result