The previous SQL query caused a full table scan of the 'trans' table at startup.

I used git-diff for each file and concatenated the result to preverse the order.

This fixes invalid next_serial entries in cache,
and the following error for values not in cache:

  Traceback (most recent call last):
    File "ZODB/Connection.py", line 856, in setstate
      self._setstate(obj)
    File "ZODB/Connection.py", line 894, in _setstate
      self._load_before_or_conflict(obj)
    File "ZODB/Connection.py", line 922, in _load_before_or_conflict
      if not self._setstate_noncurrent(obj):
    File "ZODB/Connection.py", line 945, in _setstate_noncurrent
      assert end is not None
  AssertionError

When run with MySQL, testBasicStore (neo.tests.threaded.test.Test) was slow
and generated log exceeded 29MB.

This increases the number of rows to check per AskCheck*Range packets.

And document 3 bugs found by running many times testBackupNodeLost. About the
tic() issue, I had a case where the test exited instead of looping forever after
the storage crash.

Before, it was only done for 'logfile'.

- Review error handling. Only 2 exceptions remain in connector.py:

  - Drop useless exception handling for EAGAIN since it should not happen
    if the kernel says the socket is ready.
  - Do not distinguish other socket errors. Just close and log in a generic way.
  - No need to raise a specific exception for EOF.
  - Make 'connect' return a boolean instead of raising an exception.
  - Raise appropriate exception when answer/ask/notify is called on a closed
    non-MT connection.

- Add support for more complex connectors, which may need to write for a read
  operation, or to read when there's pending data to send. This will be
  required for SSL support (more exactly, the handshake will be done in
  a transparent way):

  - Move write buffer to connector.
  - Make 'receive' fill the read buffer, instead of returning the read data.
  - Make 'receive' & 'send' return a boolean to switch polling for writing.
  - Tolerate that sockets return 0 as number of bytes sent.

- In testConnection, simply delete all failing tests, as announced
  in commit 71e30fb9.

Application will hold SSL parameters.

This frees a reference to the last handler and there's no need to make the
instance reusable.

This follows the behaviour of FileStorage.

There remain only one leak in ClientApplicationTests.test_connectToPrimaryNode
because of Mock objects.

admin: do not reset the list of known masters from configuration (or command line) when reconnecting

This is questionable but a lot of NodeManager must be reviewed if we want to do
differently. At least, admin nodes now behave like clients.

It's been a long time that the polling thread never ends and don't need to be
restarted. On the other side, there will be a need for the admin to define a
different polling loop, hence the move from threaded_poll to threaded_app.

It was still used to stop a cluster.

This makes tests easier to write, with more determinism.
If only I had the idea to monkey-patch SimpleQueue several years ago.

The previous implementation was built around a 'pending' global variable that
was set by a few monkey-patches when some network activity was pending between
nodes. All this is replaced by an extra epoll object is used to wait for nodes
that have pending network events: this is simpler, and faster since it
significantly reduces the number of context switches.

This is a regression caused by commit eef52c27
("Tickless poll loop, for lowest latency and cpu usage"), affecting:
- admins
- storages
- primary masters of backup clusters

Recent Python already catches exceptions due to garbage collection on exit.