[IMP] models: add the base model as an abstract model in the registry

The model `base` is implicitly inherited by all models, and can be extended as
any other model.

openerp/addons/base/ir/ir_model.py

@@ -50,6 +50,13 @@ def _in_modules(self, cr, uid, ids, field_name, arg, context=None):
         result[k] = ', '.join(sorted(installed_modules & set(xml_id.split('.')[0] for xml_id in v)))
     return result
 
+#
+# IMPORTANT: this must be the first model declared in the module
+#
+class Base(models.AbstractModel):
+    """ The base model, which is implicitly inherited by all models. """
+    _name = 'base'
+
 class unknown(models.AbstractModel):
     """
     Abstract model used as a substitute for relational fields with an unknown

openerp/models.py

@@ -612,6 +612,10 @@ class BaseModel(object):
         # determine the model's name
         name = cls._name or (len(parents) == 1 and parents[0]) or cls.__name__
 
+        # all models except 'base' implicitly inherit from 'base'
+        if name != 'base':
+            parents = list(parents) + ['base']
+
         # create or retrieve the model's class
         if name in parents:
             if name not in pool: