pylint #8769 downgrads missing attribute errors to warnings if there is some modifications to __dict__ or __getattr__ [open]

Idea proposed to Vincent Legoll, since we know pylint/astng won't ever be able to read dynamic code such as :

class struct(object):
   """Similar to a dictionary except that members may be accessed as
   s.member.
   Usage:
   s = struct(a=10, b=20, d={"cat":"dog"} )
  print s.a + s.b
   """
   def __init__(self, **args):
       self.__dict__.update(args)
   def __repr__(self):
       r = ["<"]
       for i in self.__dict__.keys():
           r.append("%s=%s" % (i, getattr(self,i)))
       r.append(">\n")
       return " ".join(r)