title: "Add New Constraints" checkboxes and fields are disabled
body: <p>I have a project I am upgrading from Xcode 4.6.3 to Xcode 6.1.1.  I opened it in Xcode 6.1.1, and opened each .xib.  The format of each .xib changed as expected.  I want to attempt to use auto layout.  Use Auto Layout is checked and so is Use Size Classes.  I changed every appropriate object from Alignment Frame to be Alignment Rectangle.  </p>
  
  <p>For a while I couldn’t add any constraints.  Then after some trying I could add a few.  See the screenshot.<br>
  <img src="https://i.stack.imgur.com/fHQIE.png" alt="enter image description here">
  For the selected View, I cannot add a constraint.  The Add New Constraints checkboxes and fields are disabled.  Only Update Frames is available to be changed.  I can’t add an alignment constraint either.  Ctrl-drag a line off the view does not add a constraint either.  Notice the View height of 411.  If I select another object, then select the View again the height will change to be the height of the parent tab bar less.  If I keep doing that the height gets smaller and smaller, then Xcode crashes.  How can I add a constraint to this view?</p>
  
  <p>The Tab Bar X, Y, Width, and Height are disabled.  When I change the Height of the Assigned View Controller View, the Tab Bar Y changes to that value minus the Tab Bar Height of 49.  When I select the View, again it’s Height is now 49 less.  Select the Tab Bar, it’s Y is now 49 less.  And so on.  How do I set the dimensions of the Assigned View Controller View that will stick when I cannot add contraints?</p>