title: Openerp says an existing model does not exist in a many2many relation
body: <p>I'm trying to establish a many2many relation between my model and account.tax.</p>
  
  <p>I'm using the following column definition: </p>
  
  <pre><code>'tax_id': fields.many2many('account.tax', 'account_contract_line_tax', 'contract_line_id', 'tax_id', 'Taxes', domain=[('parent_id','=',False)]),
  </code></pre>
  
  <p>And I'm getting the following erorr:</p>
  
  <pre><code>2014-05-25 16:18:55,456 31937 ERROR ***_dev openerp.netsvc: Programming Error
  Many2Many destination model does not exist: `account.tax`
  Traceback (most recent call last):
    File "/usr/lib/pymodules/python2.7/openerp/netsvc.py", line 292, in dispatch_rpc
      result = ExportService.getService(service_name).dispatch(method, params)
    File "/usr/lib/pymodules/python2.7/openerp/service/web_services.py", line 622, in dispatch
      security.check(db,uid,passwd)
    File "/usr/lib/pymodules/python2.7/openerp/service/security.py", line 40, in check
      pool = pooler.get_pool(db)
    File "/usr/lib/pymodules/python2.7/openerp/pooler.py", line 49, in get_pool
      return get_db_and_pool(db_name, force_demo, status, update_module)[1]
    File "/usr/lib/pymodules/python2.7/openerp/pooler.py", line 33, in get_db_and_pool
      registry = RegistryManager.get(db_name, force_demo, status, update_module)
    File "/usr/lib/pymodules/python2.7/openerp/modules/registry.py", line 203, in get
      update_module)
    File "/usr/lib/pymodules/python2.7/openerp/modules/registry.py", line 233, in new
      openerp.modules.load_modules(registry.db, force_demo, status, update_module)
    File "/usr/lib/pymodules/python2.7/openerp/modules/loading.py", line 350, in load_modules
      force, status, report, loaded_modules, update_module)
    File "/usr/lib/pymodules/python2.7/openerp/modules/loading.py", line 256, in load_marked_modules
      loaded, processed = load_module_graph(cr, graph, progressdict, report=report, skip_modules=loaded_modules, perform_checks=perform_checks)
    File "/usr/lib/pymodules/python2.7/openerp/modules/loading.py", line 165, in load_module_graph
      init_module_models(cr, package.name, models)
    File "/usr/lib/pymodules/python2.7/openerp/modules/module.py", line 374, in init_module_models
      result = obj._auto_init(cr, {'module': module_name})
    File "/usr/lib/pymodules/python2.7/openerp/osv/orm.py", line 3028, in _auto_init
      self._m2m_raise_or_create_relation(cr, f)
    File "/usr/lib/pymodules/python2.7/openerp/osv/orm.py", line 3338, in _m2m_raise_or_create_relation
      raise except_orm('Programming Error', 'Many2Many destination model does not exist: `%s`' % (f._obj,))
  except_orm: ('Programming Error', 'Many2Many destination model does not exist: `account.tax`')
  </code></pre>
  
  <p>Of course, account.tax is existing since I'm using the ERP to established invoice with account module. Furthermore, I can see the model in configuration/database structure/model</p>
  
  <p>I nearly copied the line from account module...</p>
  
  <p>Any ideas ?</p>
  
  <p>A.</p>