There was a sign error in the formula and it lacks code to deal with clock
changes.
Because the watcher will be removed, this patch reverts to imprecise but safe
and simple implementation.

Relevant race condition is between recursiveReindexObject and
unindexObject (triggered by setId).

Change listbox to display the portal_type in the column Type and add a new column to display the resource_title

Products.ERP5Type.JSONEncoder is deprecated in favour of 'json' module,
which is already tested by Python.

Messages passed to a grouping method are not sorted.

* fix jquery.js location
* field title should be string

This fixes test_report_view (testDeferredStyle).

memcache module already handle thread-safety, and we actually want to be
transaction-local here, so use a volatile variable instead for caching
needs.
Removes the need to restart Zope for connection parameter changes to take
effect.
Fixes a bad interaction with SelectionTool's code, which causes
transactional isolation to be broken (just for this connector) and too many
network connections to be used.

Garbage-collecting memcache.Client instance does that automatically.

Docstrings are not to annotate what code is doing.

Concurrency handling is not required, because a single MemcachedDict should
not be accessed outside a Zope transaction, which is itself bound to a
specific thread.
Pickling a connection is not needed, ERP5Type.Core.MemcachedPlugin is all
we need to serialise.

Simplifies code creating a new connection.

Doc's mention about expiration time is precisely that server's code is
supposed to do just that internally.

See commit 4718f5e1