[FIX] hr_contract: count the number of contracts of an employee as superuser_id as this field is required in the form view. However no data is displayed, and no data about the contracts are leaked, so no security holes.
[FIX] fields: convert_to_cache() on *2many fields must take record's current value

The existing code was buggy when writing on *2many fields with a list of
commands: the value was converted for the cache, but taking an empty recordset
as the current value of the field.
[FIX] project_issue: reviewer_id doesn(t exist

(partial revert of 44a5268c00443cfb0664d7679d93772422a7403)
[FIX] base: fixes #1167, change password wizard (wrong default value)

The one2many field 'user_ids' was initialized with an incorrect value for the
inverse field 'wizard_id', using a res.users id. The latter was causing a
MissingError exception. The fix is simply to not define explicitly the inverse
field in the one2many.

Also did a small cleanup of the code of the wizard.
[FIX] stock: typo when selecting inventory on single product
[FIX] Exporting of res.partner works again

Singleton object was required while access model properties, but search returns multiple results and hence caused traceback while accessing record.property
[FIX] website_livechat: reference of demo data was preventing to install the module

Added a record of im_livechat.channel in website_livechat data
[FIX] Allow search on `_inherits` fields.

As `_inherits` fields are now handled via `related`
fields (not stored, obviously), a new descriptor
`searchable` has been added to `fields_get()` result
to indicated if the field is searchable or not.
[IMP] fields: add mechanism to extend a selection field

If a selection field is defined by a list as selection, such as:

    state = fields.Selection([('a', 'A'), ('b', 'B')])

one can extend it by inheritance by redefining the field, as:

    state = fields.Selection(selection_add=[('c', 'C')])

The result is that the selection field will have the list
[('a', 'A'), ('b', 'B'), ('c', 'C')] as selection.
[IMP] models: name_search() should call _name_search()

This avoids code duplication between methods, and keeps backward compatibility
with existing code overriding _name_search().
[FIX] web: make search by `id` possible.

+ correct tests