Merge FileStorageError change to 2.7 branch

[ChrisW]

[Tim Peters]

>>>>>> If you're using a current ZODB (anything at or after 3.2.1c1;
>>>>>> 3.2.5 is the latest stable release in the 3.2 line), an attempt to
>>>>>> pack to a time earlier than the most recent time ever packed to
>>>>>> shouldn't do anything more than raise a FileStorageError with
>>>>>> this detail:
>>>>>>
>>>>>> The database has already been packed to a later time
>>>>>> or no changes have been made since the last pack

[Chris Withers]

>>>> I'm sure I remember discussions where it was agreed that this
>>>> annoying behaviour would be dropped?
>>>> (or at least turned into a subclass that could be easily caught,
>>>> rathe than having to catch FileStorageError and then do a string
>>>> comparison o the exception arguments :-( )

[Tim]

>> It was changed (to log a message instead). I see that it's in ZODB
>> 3.3 (under svn), but not on the Zope-2_7-branch branch of ZODB3 (under
>> CVS). Don't know what happened there. Looks like we're missing
>> several changes that were checked in -- maybe they're only on ZODB3
>> HEAD? Something's screwed up here indeed.

After more staring, same story: the changes are in ZODB 3.3 (used
with Zope 2.8 and Zope 3), but not on CVS's Zope-2_7-branch branch of
ZODB3. I don't intend to address anything other than critical
bugfixes in the ZODB 3.2 line anymore, so I don't intend to change
this. If someone else wants to merge in this specific change on
Zope-2_7-branch, that would be OK by me.

[Hanno Schlichting (hannosch)]

The mentioned merging problems have been resolved in the end. At least "The database has already been packed..." is not a FileStorageError today.