Remove PyUnicode_ClearFreeList() function: the Unicode free list has
been removed in Python 3.3.

Remove PyMethod_ClearFreeList() and PyCFunction_ClearFreeList()
functions: the free lists of bound method objects have been removed.

Remove also _PyMethod_Fini() and _PyCFunction_Fini() functions.

* Rename _PyGC_InitializeRuntime() to _PyGC_InitState()
* finalize_interp_clear() now also calls _PyGC_Fini() in
  subinterpreters (clear the GC state).

* Add GCState type for readability
* gcmodule.c now gets its gcstate from tstate
* _PyGC_DumpShutdownStats() now expects tstate rather than runtime
* Rename "state" to "gcstate" for readability: to avoid confusion
  between "state" and "tstate" for example.
* collect() now only expects tstate: it gets gcstate from tstate.
* Pass tstate to _PyErr_xxx() functions

* Factorize code in common between Py_FinalizeEx() and
  Py_EndInterpreter().
* Py_EndInterpreter() now also calls _PyWarnings_Fini().
* Call _PyExc_Fini() and _PyGC_Fini() later in the finalization.

Add PyInterpreterState.runtime field: reference to the _PyRuntime
global variable. This field exists to not have to pass runtime in
addition to tstate to a function.  Get runtime from tstate:
tstate->interp->runtime.

Remove "_PyRuntimeState *runtime" parameter from functions already
taking a "PyThreadState *tstate" parameter.

_PyGC_Init() first parameter becomes "PyThreadState *tstate".

Pass tstate parameter (PyThreadState) to GC collect() function and
other GC subfunctions.

* Rename _PyGC_Initialize() to _PyGC_InitializeRuntime()
* Add _PyGC_Init(): initialize _PyRuntime.gc.garbage list
* Call _PyGC_Init() before _PyTypes_Init()