Now OpenERPSession is a subclass of werkzeug's session
Completely removed all ways to specify session identifiers and reduced them to 2 possibilities:

* The http argument 'session_id' (higher priority)
* The cookie 'session_id' (lower priority)
more and more cleaning
Renamed all _shit in session to remove the underscore
Make the server always check the identity of the logged user and switch default values of db, uid, login and password to None
Some details + documentation
Forgot some refactoring
Solved a problem appearing in share module
[IMP] Important changes to the OpenERPSession server-side class and the way the web client handles sessions. Mostly:

* The OpenERPSession class now extends the werkzeug's session class, and is now the only class used to handle sessions
* Now only one cookie is used to identify the session: session_id . It is also possible to specify the id by adding the
  http parameter session_id (the http parameter has higher priority than the cookie).