Revert SnapKit#574

Source/LayoutConstraint.swift

@@ -44,36 +44,17 @@ public class LayoutConstraint : NSLayoutConstraint {
 }
 
 internal func ==(lhs: LayoutConstraint, rhs: LayoutConstraint) -> Bool {
-    #if os(OSX)
-    // ensure first anchor items match
-    guard let item1 = lhs.firstAnchor.item,
-          let item2 = rhs.firstAnchor.item,
-          item1 === item2 else {
-        return false
-    }
-
-    // ensure second anchor items match
-    guard ((lhs.secondAnchor?.item == nil && rhs.secondAnchor?.item == nil) ||
-           (lhs.secondAnchor?.item === rhs.secondAnchor?.item)) else {
-        return false
-    }
-    #else
-    guard lhs.firstAnchor == rhs.firstAnchor else {
-        return false
-    }
-    guard ((lhs.secondAnchor == nil && rhs.secondAnchor == nil) ||
-           (lhs.secondAnchor! == rhs.secondAnchor!)) else {
-        return false
-    }
-    #endif
-
-
-    // ensure attributes, relation, priorty and multiplier match
+    // If firstItem or secondItem on either constraint has a dangling pointer
+    // this comparison can cause a crash. The solution for this is to ensure
+    // your layout code hold strong references to things like Views, LayoutGuides
+    // and LayoutAnchors as SnapKit will not keep strong references to any of these.
     guard lhs.firstAttribute == rhs.firstAttribute &&
           lhs.secondAttribute == rhs.secondAttribute &&
           lhs.relation == rhs.relation &&
           lhs.priority == rhs.priority &&
-          lhs.multiplier == rhs.multiplier else {
+          lhs.multiplier == rhs.multiplier &&
+          lhs.secondItem === rhs.secondItem &&
+          lhs.firstItem === rhs.firstItem else {
         return false
     }
     return true