Try to get ring.h installed.

NEWS.txt

@@ -17,6 +17,12 @@ impossible to overlook.  In a release build, ``unghostify()`` raises
 problem in a release build (``ghostify()`` is supposed to be so simple that
 it "can't fail").
 
+Install
+-------
+
+The C header file ``ring.h`` is now installed.
+
+
 What's new in ZODB3 3.3?
 ========================
 Release date: 06-Oct-2004

setup.py

@@ -229,7 +229,8 @@ setup(name="ZODB3",
       packages = packages,
       package_dir = {'': 'src'},
       ext_modules = exts,
-      headers = ['src/persistent/cPersistence.h'],
+      headers = ['src/persistent/cPersistence.h',
+                 'src/persistent/ring.h'],
       license = "ZPL 2.1",
       platforms = ["any"],
       description = doclines[0],