ais_py.cpp: Py_DECREF lists once inserted in dicts.

[lsix]

Along the creation of python dict, few lists are created and then inserted into the dict using PyDict_SetItemString/DictSafeSetItem. The latter internaly uses PyDict_SetItemString. This function does not steal a reference to its VAL argument, i.e. it increments the refcount of the list.

Once this is done, a call to Py_DECREF should be made to indicate that the c++ code does not own the list anymore. Not doing so caused few memory leaks.

[lsix]

I have rebased this PR as well.

[schwehr]

Thanks for the fixes!