New functionnalities

--------------------

* Add Zmq server, based on the cutting edge ZMQ (http://www.zeromq.org/) socket

  library.  This allows to access distant instance, in a similar way as Pyro.

* Publish/subscribe mechanism using ZMQ for communication among cubicweb

  instances.  The new zmq-address-sub and zmq-address-pub configuration variables

  define where this communication occurs.  As of this release this mechanism is

  used for entity cache invalidation.

* Improved WSGI support. While there is still some caveats, most of the code

  which was twisted only is now generic and allows related functionalities to work

  with a WSGI front-end.

* Full undo/transaction support : undo of modification has eventually been

  implemented, and the configuration simplified (basically you activate it or not

  on an instance basis).

* Controlling HTTP status code used is not much more easier :

  - `WebRequest` now has a `status_out` attribut to control the response status ;

  - most web-side exceptions take an optional ``status`` argument.

API changes

-----------

* The base registry implementation has been moved to a new

  `logilab.common.registry` module (see #1916014). This includes code from :

  * `cubicweb.vreg` (the whole things that was in there)

  * `cw.appobject` (base selectors and all).

  In the process, some renaming was done:

  * the top level registry is now `RegistryStore` (was `VRegistry`), but that

    should not impact cubicweb client code ;

  * former selectors functions are now known as "predicate", though you still use

    predicates to build an object'selector ;

  * for consistency, the `objectify_selector` decoraror has hence be renamed to

    `objectify_predicate` ;

  * on the CubicWeb side, the `selectors` module has been renamed to

    `predicates`.

  Debugging refactoring dropped the more need for the `lltrace` decorator.  There

  should be full backward compat with proper deprecation warnings.  Notice the

  `yes` predicate and `objectify_predicate` decorator, as well as the

  `traced_selection` function should now be imported from the

  `logilab.common.registry` module.

* All login forms are now submitted to <app_root>/login. Redirection to requested

  page is now handled by the login controller (it was previously handle by the

  session manager).

* `Publisher.publish` has been renamed to `Publisher.handle_request`. This

  method now contains generic version of logic previously handled by

  Twisted. `Controller.publish` is **not** affected.

Unintrusive API changes

-----------------------

* New 'ldapfeed' source type, designed to replace 'ldapuser' source with

  data-feed (i.e. copy based) source ideas.

* New 'zmqrql' source type, similar to 'pyrorql' but using ømq instead of Pyro.

* A new registry called `services` has appeared, where you can register

  server-side `cubicweb.server.Service` child classes. Their `call` method can be

  invoked from a web-side AppObject instance using new `self._cw.call_service`

  method or a server-side one using `self.session.call_service`. This is a new

  way to call server-side methods, much cleaner than monkey patching the

  Repository class, which becomes a deprecated way to perform similar tasks.

* a new `ajax-func` registry now hosts all remote functions (i.e. functions

  callable through the `asyncRemoteExec` JS api). A convenience `ajaxfunc`

  decorator will let you expose your python function easily without all the

  appobject standard boilerplate. Backward compatibility is preserved.

* the 'json' controller is now deprecated in favor of the 'ajax' one.

* `WebRequest.build_url` can now take a __secure__ argument. When True cubicweb

  try to generate an https url.

User interface changes

----------------------

A new 'undohistory' view expose the undoable transactions and give access to undo

some of them.