Since in ZODB TIDs are corresponding to time, provide functionality to
convert a tid to timestamp. Do so in exactly the same way as ZODB/py
does for interoperability.

Our path of implementing NEO in Go will be not only for server-side, but
also for client-side, since it is needed by Wendelin.core. On
server-side we'll also need to work with types and data model Python
ZODB implementation uses, so here it goes: Start of ZODB in Go.

Here we define ZODB data types, data model and operational interfaces
for IStorage + friends.

The interfaces are currently read-only with stubs for write mode.

Ignore files commonly produced while profiling Go programs and running
tests.

We want to make sure the code can be used by all projects without a
problem. This way the license is GPLv3+ with wide exception for all Free
Software / Open Source projects + Business options.

Nexedi stack is licensed under Free Software licenses with various exceptions
that cover three business cases:

- Free Software
- Proprietary Software
- Rebranding

As long as one intends to develop Free Software based on Nexedi stack, no
license cost is involved. Developing proprietary software based on Nexedi stack
may require a proprietary exception license. Rebranding Nexedi stack is
prohibited unless rebranding license is acquired.

Through this licensing approach, Nexedi expects to encourage Free Software
development without restrictions and at the same time create a framework for
proprietary software to contribute to the long term sustainability of the
Nexedi stack.

Please see https://www.nexedi.com/licensing for details, rationale and options.

( NEO/py for now stays at the old terms but it will be upgraded to the same
  terms as NEO/go eventually )

Sync with current NEO in Python implementation as the first step.

We'll be using some common bits and in particular on-the-wire protocol
must be the same and for py/go interoperability testing we'll also need
python parts.

This information is handy to see how well cache performs.

Amended by Julien Muchembled:
- do not abbreviate some existing field names in repr result (asking the
  user to look at the source code in order to decipher logs is not nice)
- hit: change from %.1f to %.3g
- hit: hide it completely if nload is 0
- use __future__.division instead of adding more casts to float

INFO Z2 Log files reopened successfully
INFO SignalHandler Caught signal SIGTERM
INFO Z2 Shutting down fast
INFO ZServer closing HTTP to new connections
ERROR ZODB.Connection Couldn't load state for BTrees.LOBTree.LOBucket 0xc12e29
Traceback (most recent call last):
  File "ZODB/Connection.py", line 909, in setstate
    self._setstate(obj, oid)
  File "ZODB/Connection.py", line 953, in _setstate
    p, serial = self._storage.load(oid, '')
  File "neo/client/Storage.py", line 81, in load
    return self.app.load(oid)[:2]
  File "neo/client/app.py", line 355, in load
    data, tid, next_tid, _ = self._loadFromStorage(oid, tid, before_tid)
  File "neo/client/app.py", line 387, in _loadFromStorage
    askStorage)
  File "neo/client/app.py", line 297, in _askStorageForRead
    self.sync()
  File "neo/client/app.py", line 898, in sync
    self._askPrimary(Packets.Ping())
  File "neo/client/app.py", line 163, in _askPrimary
    return self._ask(self._getMasterConnection(), packet,
  File "neo/client/app.py", line 177, in _getMasterConnection
    result = self.master_conn = self._connectToPrimaryNode()
  File "neo/client/app.py", line 202, in _connectToPrimaryNode
    index = (index + 1) % len(master_list)
ZeroDivisionError: integer division or modulo by zero

It's not possible yet to replicate a node that is importing data.
One must wait that the migration is finished.

The project to implement NEO storage and probably other pieces in Go
with the goal to have much lower request-reply latencies and
much better scalability when serving many clients compared to NEO
implemented in Python.

This reverts commit d3c22487 partially
and fixes the bug in a much simpler way.

Traceback (most recent call last):
  [...]
  File "neo/storage/handlers/client.py", line 115, in askStoreObject
    *e.args)
  File "neo/lib/handler.py", line 333, in queueEvent
    self.sortQueuedEvents()
  File "neo/lib/handler.py", line 326, in <lambda>
    self._event_queue.sort(key=key))()
  File "neo/storage/transactions.py", line 67, in __lt__
    return self.locking_tid < other.locking_tid
AttributeError: 'NoneType' object has no attribute 'locking_tid'

Pending events:
  (None, <askFetchTransactions: ...>)
  (<Transaction(C13, locking_tid=03c266508a058388, tid=None, age=0.21s) at 0x7f086bbc3d50>, <_askStoreObject: ...>)

It was out-of-date since commit 23b6a66a.

This time we had issues with _getObject and getReplicationObjectList
on production.
It seems related to the upgrade of MariaDB, from 10.0.21 to 10.1.25.

See also commits eaa00a88
             and 13911ca3

The explanation became wrong during a git-rebase, when it was decided
to keep the old code that drop partitions. The new one needs more work
and it is kept in a branch.