Fixed to work with transaction 2.0.3.

Simplify the README file to avoid out of date information

We have the same information scattered around in different places,
which increases the chance that some of it will be out of date.

See the end of:
https://groups.google.com/forum/#!topic/zodb/fy6RRVAF9-s

I want to try to avoid duplicating zodb.org.

Clear Connection.transaction_manager on close. Fixes #114 for ZODB 4.

Call _p_resolveConflict() even if a conflicting change doesn't change the state

This reverts to the behaviour of 3.10.3 and older.

checkTransactionalUndoIterator: do not expect iterator to return sorted oids

fstail: print the txn offset and header size, instead of only the data offset

Before:

    2016-07-01 09:41:50.416574: hash=d7101c5ee7b8e412d7b6d54873204421e09b7f34
    user='' description='' length=1629 offset=58990284

After:

    2016-07-01 09:41:50.416574: hash=d7101c5ee7b8e412d7b6d54873204421e09b7f34
    user='' description='' length=1629 offset=58990261 (+23)

The structure of a FileStorage DB is such that it's easy to revert the last
transactions, by truncating the file at the right offset. With the above
change, `fstail` can now be used to get this offset.

In the above example:

    truncate -s 58990261 Data.fs

would delete the transaction and all those after.

Refactored FileStorage transactional undo

Fix handle_all_serials for the new and old protocols.

As part of a project to provide object-level commit locks for ZEO, I'm
refactiring FileStorage to maintain transaction-specific data in
Tranaction.data.  This involved undo.  In trying to figure this out, I
found:

- A bug in _undoDataInfo, which I verified with some tests and

- _transactionalUndoRecord was maddeningly difficult to reason about
  (and thus change).

I was concerned less by the bug than my inability to know whether a
change to the code would be correct.

So I refactored the code, mainly transactionalUndoRecord, to make the
code easier to understand, fixing some logic errors (I'm pretty sure)
along the way.  This included lots of comments. (Comments are much
easier to compose when you're working out logic you didn't
understand.)

In addition to makeing the code cleaner, it allows undo to be handled
in cases that weren't handled before.

Only tpc_vote can report resolved conflicts with the new commit protocol

Better support of the new API to notify of resolved conflicts (store/tpc_finish)

Conflicts:
	src/ZODB/interfaces.py

ZEO handles undo asynchronously and ZODB has for some time allowed
undo oids to be returned via vote.

Define a new interface for storages that support the new commit protocol.