This uses bytes_as_strings=True option introduced in zodbpickle 0.2 for
this purpose.

This way pickles produced on Python 3 are nearly the same as on Python 2.
There are some slight differences (Python 3 seems to perform more
memoizations which grows the size of some pickles by a couple of bytes),
but they're immaterial.

Now we can use zodbpickle's noload() on Python 3 to scan pickles for
persistent references.  We couldn't do that before, because Python 3
normally pickles byte strings as calls to codecs.encode(u'latin1-data',
'latin-1'), and noload() doesn't interpret the REDUCE opcode involved in
that representation.

Note that when you're pickling byte strings using bytes_as_strings=True,
you have to load them using encoding='bytes' (which breaks instances, so
cannot be used) or using errors='bytes' (which mean some bytestrings may
get unpickled as unicode instead).  I've tried hard to discover every
place that unpickles OIDs and added conversion to bytes in those places.

Applications dealing with binary data be prepared to handle bytestrings
that unexpectedly become unicode on unpickling.  That's the price of
Python 2 compatibility.

Since now we need to pass an extra argument to loads() and Unpickler(),
but only on Python 3, the old way of ``from ZODB._compat import pickle``
no longer pays out, and I had to import the names directly.

Thanks to Martin v. Loewis for having done some of the initial lifting
for a DZUG talk. I used a lot of his changes from this diff:

http://www.dcl.hpi.uni-potsdam.de/home/loewis/zodb/ZODB.diff

Applied all changes manually to make sure I do understand them and that
they are correct.

As always 90% of the work is to catch all places where we want to deal
with bytes instead of strings.

loading index data.  This leverages the new fsBucket toString and
fromString methods and provides much faster FileStorage index saving and loading
and smaller index files.  On my machine, saves are 5 times faster and
loads are 20 times faster (after a save, when data are in disk
cache).  Indexes are roughly 30% smaller.

The index format has changed.  Old indexes can be read just fine, but
new indexes won't be readable by older versions of ZODB.

Add a record iteration protocol to FileStorage.  You can use the record iterator to iterate over all current revisions
of data pickles in the storage.

In order to support calling via ZEO, we don't implement this as an actual iterator.  An example of using the record iterator
protocol is as follows:

storage = FileStorage('anexisting.fs')
next_oid = None
while 1:
    oid, tid, data, next_oid = storage.record_iternext(next_oid)
    # do something with oid, tid and data
    if next_oid is None:
        break

The behavior of the iteration protocol is now to iterate over all current records in the database in ascending oid order, 
although this is not a promise to do so in the future.

Port from ZODB 3.2.

Give fsIndex an efficient maxKey() implementation.

This will (in a later checkin) be used to give FileStorage an "obviously
correct" way to determine the largest oid used in an .fs.index file.

Use 0/1 instead of True/False, since none of the other code uses
True/False.