Zodbupdate

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- Skip records for ZODB.blob when migrating database to Python 3 to not break
references to blobfiles.

- When migrating databases to Python 3, do not fail when converting
attributes containing None.

- Fix tests on Python 2 with ZODB >= 5.4.0, which now uses pickle
protocol 3.

- Fix `is_broken` check for old-style class instances.

- Add support for Python 3.7.

- Drop PyPy support.

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- Support Python 2.7 and 3.4, 3.5 and 3.6 and pypy 3. Drop any older
version of Python.

- The option to the select the pickler (``--pickler``) has been
removed. This was only useful if you had extension classes with
Python 2.5 or less.

- Added an option to convert a database to Python 3.

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- More debug logging shows now the currently processed OID
(that is helpful to determine which object misses the factory).

- Support for missing factories have been improved: an error used to
occur if a pickle needed an update and contained a reference to a
missing class (not instance of this class). This case is now fixed.

- Python 2.4 is no longer supported. Please stick to version 0.3 if
you need Python 2.4 support.

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- Add an option to debug broken records.

- Add an option to skip records.

- Add an option to use Python unPickler instead of C one. This let you
debug records. As well Python unPickler let you update old ExtensionClass
records who had a special hack in the past.

- Broken interfaces are well supported now (if you did alsoProvides with them).

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- Unplickle and re-pickle the code to rename references to moved classes.
This make the script works on database created with older versions of
ZODB.

- If you are working directly with a FileStorage, POSKeyError are reported
but non-fatal.

- Remove superfluous code that tried to prevent commits when no changes
happened: ZODB does this all by itself already.

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- Add option to store the rename rules into a file.

- Don't commit transactions that have no changes.

- Load rename rules from entry points ``zodbupdate``.

- Compatibility with Python 2.4

- Rename from ``zodbupgrade`` to ``zodbupdate``.

- Add 'verbose' option.

- Improve logging.

- Suppress duplicate log messages (e.g. if the same class is missing in
multiple objects).

- Improve the updating process: rewrite pickle opcodes instead of blindly
touching a class. This also allows updating pickles that can't be unpickled
due to missing classes.