Fixed bug in new code that checked for packs to times earlier than

previous packs. Packs to earlier times can cause data lossage.

src/ZODB/FileStorage.py

@@ -184,7 +184,7 @@
 #   may have a back pointer to a version record or to a non-version
 #   record.
 #
-__version__='$Revision: 1.43 $'[11:-2]
+__version__='$Revision: 1.44 $'[11:-2]
 
 import struct, time, os, bpthread, string, base64, sys
 from struct import pack, unpack
@@ -950,7 +950,7 @@ class FileStorage(BaseStorage.BaseStorage):
     def _redundant_pack(self, file, pos):
         file.seek(pos-8)
         p=u64(file.read(8))
-        file.seek(p+16)
+        file.seek(pos-p+8)
         return file.read(1) not in ' u'
 
     def pack(self, t, referencesf):
@@ -994,7 +994,8 @@ class FileStorage(BaseStorage.BaseStorage):
 
             if self._redundant_pack(file, packpos):
                 raise FileStorageError, (
-                    'The database has already been packed to a later time')
+                    'The database has already been packed to a later time\n'
+                    'or no changes have been made since the last pack')
     
             rootl=[z64]
             pop=rootl.pop