The original ml_flag of MM_push is METH_OLDARGS, which should use
PyArg_Parse. But Pyston cannot support METH_OLDARGS properly. Will
create an issue when squash this commit and last commit.

Due to the PyArg_Parse, the src is a tuple, which will cause the
self->data become something like: [({}, ), ({}, )]. The correct format
should be: [{}, {}].