title: Unexpected NSAutoresizingMaskLayoutConstraint adding UIView from nib to autolayout storyboard scene
body: <p>I've got the following in IB and both views have 'Use Auto Layout' on and 'Resizes Subviews' off.</p>
  
  <p><img src="https://i.imgur.com/ooeFwkl.png" alt="autolayout uiview"></p>
  
  <p>I'm simply trying to add an instance of Autolayout View to a container view so its edges meet its container view's edges. The container view has Uses Auto Layout on and is the same height but width is twice as much. Here's the code:</p>
  
  <pre><code>- (IBAction)addSubviewButton:(id)sender
  {
    UIView *autolayoutView = [[[NSBundle mainBundle] loadNibNamed:@"AutolayoutView" owner:nil options:nil] objectAtIndex:0];
    [self.containerView addSubview:autolayoutView];
  
    [self.containerView addConstraint:
     [NSLayoutConstraint constraintWithItem:autolayoutView
                              attribute:NSLayoutAttributeLeading
                              relatedBy:NSLayoutRelationEqual
                                 toItem:self.containerView
                              attribute:NSLayoutAttributeLeading
                             multiplier:1
                               constant:0]];
    [self.containerView addConstraint:
     [NSLayoutConstraint constraintWithItem:autolayoutView
                              attribute:NSLayoutAttributeTrailing
                              relatedBy:NSLayoutRelationEqual
                                 toItem:self.containerView
                              attribute:NSLayoutAttributeTrailing
                             multiplier:1
                               constant:0]];
    [self.containerView addConstraint:
    [NSLayoutConstraint constraintWithItem:autolayoutView
                             attribute:NSLayoutAttributeTop
                             relatedBy:NSLayoutRelationEqual
                                toItem:self.containerView
                             attribute:NSLayoutAttributeTop
                            multiplier:1.0
                              constant:0.0]];
    [self.containerView addConstraint:
    [NSLayoutConstraint constraintWithItem:autolayoutView
                             attribute:NSLayoutAttributeBottom
                             relatedBy:NSLayoutRelationEqual
                                toItem:self.containerView
                             attribute:NSLayoutAttributeBottom
                            multiplier:1.0 constant:0.0]];
  }
  </code></pre>
  
  <p>An error occurs:</p>
  
  <pre><code>Probably at least one of the constraints in the following list is one you don't want...
  (
  "&lt;NSIBPrototypingLayoutConstraint:0x8c364d0 'IB auto generated at build time for view with fixed frame' H:[UIView:0x8c356f0(275)]&gt;",
  "&lt;NSLayoutConstraint:0x8d43d80 H:|-(0)-[AutolayoutView:0x8d47a30]   (Names: '|':UIView:0x8c356f0 )&gt;",
  "&lt;NSLayoutConstraint:0x8d09260 AutolayoutView:0x8d47a30.trailing == UIView:0x8c356f0.trailing&gt;",
  "&lt;NSAutoresizingMaskLayoutConstraint:0x8d0eca0 h=--&amp; v=--&amp; AutolayoutView:0x8d47a30.midX == + 70&gt;"
  )
  </code></pre>
  
  <p>Looks like NSAutoresizingMaskLayoutConstraint is created automatically on Autolayout View after it is added as a subview? When printing Autolayout View's constraints in didMoveToSuperview, it doesn't exist yet. How can this be resolved? I wanted to try creating constraints on Autolayout View in IB as placeholders to ignore at build time but IB has all of the autolayout options disabled for Autolayout View. </p>