Flag E1101 astng inference failures

From: Daniel Drake <d.drake@mmm.com>

This is a partial workaround for #3216 in that it raises a different E1101
message when astng was unable to infer all possible object types. This allows
the potentially bogus errors to be separated from the known errors.

Index: pylint-0.12.2/checkers/typecheck.py
===================================================================
--- pylint-0.12.2.orig/checkers/typecheck.py
+++ pylint-0.12.2/checkers/typecheck.py
@@ -28,6 +28,10 @@ MSGS = {
     'E1102': ('%s is not callable',
               'Used when an object being called has been infered to a non \
               callable object'),
+    'E1103': ('%s %r has no %r member but some types could not be inferred',
+              'Used when a class is accessed for an unexistant member, but \
+              astng was not able to interpret all possible types of this \
+              class.'),
     'E1111': ('Assigning to function call which doesn\'t return',
               'Used when an assigment is done on a function call but the \
               infered function doesn\'t return anything.'),
@@ -91,9 +95,12 @@ zope\'s acquisition mecanism and so shou
         # list of (node, nodename) which are missing the attribute
         missingattr = set()
         ignoremim = self.config.ignore_mixin_members
+        inference_failure = False
         for owner in infered:
             # skip yes object
             if owner is astng.YES:
+                # but record the fact that we couldn't infer all types
+                inference_failure = True
                 continue
             # if there is ambiguity, skip None
             if len(infered) > 1 and isinstance(owner, astng.Const) \
@@ -134,7 +141,11 @@ zope\'s acquisition mecanism and so shou
                 if actual in done:
                     continue
                 done.add(actual)
-                self.add_message('E1101', node=node,
+                if inference_failure:
+                    msg = 'E1103'
+                else:
+                    msg = 'E1101'
+                self.add_message(msg, node=node,
                                  args=(display_type(owner), name,
                                        node.attrname))