Update the persistence headers.

Hashes of the files' commits in the persistent repo are as follows:

  - cPersistence.h: 8699c7fc
  - ring.h:         5364296a
  - _compat.h:      3769ede0

include/persistent/_compat.h

+/*****************************************************************************
+
+  Copyright (c) 2012 Zope Foundation and Contributors.
+  All Rights Reserved.
+
+  This software is subject to the provisions of the Zope Public License,
+  Version 2.1 (ZPL).  A copy of the ZPL should accompany this distribution.
+  THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
+  WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+  WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
+  FOR A PARTICULAR PURPOSE
+
+ ****************************************************************************/
+
+#ifndef PERSISTENT__COMPAT_H
+#define PERSISTENT__COMPAT_H
+
+#include "Python.h"
+
+#if PY_MAJOR_VERSION >= 3
+#define PY3K
+#endif
+
+#ifdef PY3K
+#define INTERN PyUnicode_InternFromString
+#define NATIVE_FROM_STRING_AND_SIZE PyUnicode_FromStringAndSize
+
+#define Py_TPFLAGS_HAVE_RICHCOMPARE 0
+
+#define INT_FROM_LONG(x) PyLong_FromLong(x)
+#define INT_CHECK(x) PyLong_Check(x)
+#define INT_AS_LONG(x) PyLong_AS_LONG(x)
+#define CAPI_CAPSULE_NAME "persistent.cPersistence.CAPI"
+
+#else
+#define INTERN PyString_InternFromString
+#define NATIVE_FROM_STRING_AND_SIZE PyString_FromStringAndSize
+
+#define INT_FROM_LONG(x) PyInt_FromLong(x)
+#define INT_CHECK(x) PyInt_Check(x)
+#define INT_AS_LONG(x) PyInt_AS_LONG(x)
+#endif
+
+#endif

include/persistent/cPersistence.h

 /*****************************************************************************
 
-  Copyright (c) 2001, 2002 Zope Corporation and Contributors.
+  Copyright (c) 2001, 2002 Zope Foundation and Contributors.
   All Rights Reserved.
 
   This software is subject to the provisions of the Zope Public License,
@@ -15,17 +15,20 @@
 #ifndef CPERSISTENCE_H
 #define CPERSISTENCE_H
 
-#include "Python.h"
+#include "_compat.h"
+#include "bytesobject.h"
+
 #include "ring.h"
 
 #define CACHE_HEAD \
     PyObject_HEAD \
     CPersistentRing ring_home; \
-    int non_ghost_count;
+    int non_ghost_count; \
+    PY_LONG_LONG total_estimated_size;
 
 struct ccobject_head_struct;
 
-typedef struct ccobject_head_struct PerCache;
+typedef struct ccobject_head_struct PerCache;    
 
 /* How big is a persistent object?
 
@@ -36,13 +39,14 @@ typedef struct ccobject_head_struct PerCache;
     8  ring struct
     8  serialno
     4  state + extra
+    4  size info
 
-  (52) so far
+  (56) so far
 
     4  dict ptr
     4  weaklist ptr
   -------------------------
-   64  only need 62, but obmalloc rounds up to multiple of eight
+   68  only need 62, but obmalloc rounds up to multiple of eight
 
   Even a ghost requires 64 bytes.  It's possible to make a persistent
   instance with slots and no dict, which changes the storage needed.
@@ -56,8 +60,28 @@ typedef struct ccobject_head_struct PerCache;
     PerCache *cache; \
     CPersistentRing ring; \
     char serial[8]; \
-    signed char state; \
-    unsigned char reserved[3];
+    signed state:8;                              \
+    unsigned estimated_size:24;
+
+/* We recently added estimated_size.  We originally added it as a new
+   unsigned long field after a signed char state field and a
+   3-character reserved field.  This didn't work because there
+   are packages in the wild that have their own copies of cPersistence.h
+   that didn't see the update.  
+
+   To get around this, we used the reserved space by making
+   estimated_size a 24-bit bit field in the space occupied by the old
+   3-character reserved field.  To fit in 24 bits, we made the units
+   of estimated_size 64-character blocks.  This allows is to handle up
+   to a GB.  We should never see that, but to be paranoid, we also
+   truncate sizes greater than 1GB.  We also set the minimum size to
+   64 bytes.
+
+   We use the _estimated_size_in_24_bits and _estimated_size_in_bytes
+   macros both to avoid repetition and to make intent a little clearer.
+*/
+#define _estimated_size_in_24_bits(I) ((I) > 1073741696 ? 16777215 : (I)/64+1)
+#define _estimated_size_in_bytes(I) ((I)*64)
 
 #define cPersistent_GHOST_STATE -1
 #define cPersistent_UPTODATE_STATE 0
@@ -79,6 +103,7 @@ typedef struct {
     void (*ghostify)(cPersistentObject*);
     int (*setstate)(PyObject*);
     percachedelfunc percachedel;
+    int (*readCurrent)(cPersistentObject*);
 } cPersistenceCAPIstruct;
 
 #define cPersistenceType cPersistenceCAPI->pertype
@@ -95,6 +120,9 @@ static cPersistenceCAPIstruct *cPersistenceCAPI;
 
 #define PER_CHANGED(O) (cPersistenceCAPI->changed((cPersistentObject*)(O)))
 
+#define PER_READCURRENT(O, E)                                     \
+  if (cPersistenceCAPI->readCurrent((cPersistentObject*)(O)) < 0) { E; }
+
 #define PER_GHOSTIFY(O) (cPersistenceCAPI->ghostify((cPersistentObject*)(O)))
 
 /* If the object is sticky, make it non-sticky, so that it can be ghostified.

include/persistent/ring.h

 /*****************************************************************************
 
-  Copyright (c) 2003 Zope Corporation and Contributors.
+  Copyright (c) 2003 Zope Foundation and Contributors.
   All Rights Reserved.
 
   This software is subject to the provisions of the Zope Public License,