title: deal with many2many field in odoo
body: <p>I have two models skills and res_users.</p>
  
  <p>I want that each user can have many skills and also each skill can have many users on it. I tried to do that but without success.</p>
  
  <p>This is my skills:</p>
  
  <pre><code>class technicians_skills(osv.osv):
  _name = 'skills'
  _description = 'Technicians Skills'
  
  _columns = {
      'name': fields.char(string='name', size=50),
      'description': fields.text(string="description"),
      'member_ids': fields.many2many('res.users', 'skill', string='Technicians')
  } 
  </code></pre>
  
  <p>and this is the users :</p>
  
  <pre><code>class res_users(osv.osv):
  _inherit = 'res.users'
  
  _columns = {
     'skill': fields.many2many('skills', relation='skills.rel', column1='name', column2='skill', string='Skill'),
  }
  </code></pre>
  
  <p>and I want to know the skills of each user, but when I call this :</p>
  
  <pre><code>test = http.request.env['skills.rel'].search([])
  </code></pre>
  
  <p>It shows me this error</p>
  
  <blockquote>
    <p>KeyError: 'skills.rel'</p>
  </blockquote>