Merge rev 28660 from 3.3 branch.

More code and comment cleanups.  Notable changes:

FileCache:  removed the currentsize attribute.  It was initialized
to 0 but never updated.  Some tests referenced it, but since it was
always 0 those tests weren't getting any good from it.  Don't
recall (or never knew) what its intended purpose may have been.

FileCache.remove():  Repaired major bug.  This mistakenly stored
the "this disk block is free now" status byte into the start of
the serialized Object record's end_tid field (incorrect seek
offset).  The in-memory structures were correct then, but got out
of synch with the disk file; the latter then still claimed to have
info for a "live" object revision, but that revision was actually
dead, and the info on disk had a corrupt end_tid value.

NEWS.txt

@@ -55,6 +55,12 @@ What's new in ZODB3 3.3.1?
 ==========================
 Release date: xx-xxx-2004
 
+ZEO client cache
+----------------
+
+- Fixed a bug wherein an object removed from the client cache didn't
+  properly mark the file slice it occupied as being available for reuse.
+
 persistent
 ----------
 

src/ZEO/tests/test_cache.py

@@ -114,13 +114,11 @@ class CacheTests(unittest.TestCase):
             n = p64(i)
             self.cache.store(n, "", n, None, data[i])
             self.assertEquals(len(self.cache), i + 1)
-            self.assert_(self.cache.fc.currentsize < maxsize)
         # The cache now uses 1225 bytes.  The next insert
         # should delete some objects.
         n = p64(50)
         self.cache.store(n, "", n, None, data[51])
         self.assert_(len(self.cache) < 51)
-        self.assert_(self.cache.fc.currentsize <= maxsize)
 
         # XXX Need to make sure eviction of non-current data
         # and of version data are handled correctly.