-[UIView addSubnode:], -[CALayer addSubnode:].

Bring back this convenience API -- it disappeared somewhere along the
line while we were building Paper.  This is totally trivial, but
conveniently won't break if you layer-back a leaf node.

Closes #278.

AsyncDisplayKit/ASDisplayNode.h

@@ -520,3 +520,19 @@ typedef CALayer *(^ASDisplayNodeLayerBlock)();
  */
 @interface ASDisplayNode (ASDisplayNodeAsyncTransactionContainer) <ASDisplayNodeAsyncTransactionContainer>
 @end
+
+
+@interface UIView (AsyncDisplayKit)
+/**
+ * Convenience method, equivalent to [view addSubview:node.view] or [view.layer addSublayer:node.layer] if layer-backed.
+ */
+- (void)addSubnode:(ASDisplayNode *)node;
+@end
+
+
+@interface CALayer (AsyncDisplayKit)
+/**
+ * Convenience method, equivalent to [layer addSublayer:node.layer].
+ */
+- (void)addSubnode:(ASDisplayNode *)node;
+@end

AsyncDisplayKit/ASDisplayNode.mm

@@ -1751,3 +1751,26 @@ static const char *ASDisplayNodeAssociatedNodeKey = "ASAssociatedNode";
 @implementation CALayer (ASDisplayNodeInternal)
 @dynamic asyncdisplaykit_node;
 @end
+
+
+@implementation UIView (AsyncDisplayKit)
+
+- (void)addSubnode:(ASDisplayNode *)node
+{
+  if (node.layerBacked) {
+    [self.layer addSublayer:node.layer];
+  } else {
+    [self addSubview:node.view];
+  }
+}
+
+@end
+
+@implementation CALayer (AsyncDisplayKit)
+
+- (void)addSubnode:(ASDisplayNode *)node
+{
+  [self addSublayer:node.layer];
+}
+
+@end

examples/EditableText/Sample/ViewController.m

@@ -51,7 +51,7 @@
 {
   [super viewDidLoad];
 
-  [self.view addSubview:_textNode.view];
+  [self.view addSubnode:_textNode];
 
   [self.view addGestureRecognizer:[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(tap:)]];
 }

examples/Multiplex/Sample/ViewController.m

@@ -61,7 +61,7 @@
 {
   [super viewDidLoad];
 
-  [self.view addSubview:_imageNode.view];
+  [self.view addSubnode:_imageNode];
   [self.view addSubview:_textLabel];
 
   [self start];

examples/Placeholders/Sample/ViewController.m

@@ -89,8 +89,8 @@
   // this placeholder will cover all subnodes while they are displaying, just a like a stage curtain!
   _postNode.placeholderEnabled = NO;
 
-  [self.view addSubview:_imageNode.view];
+  [self.view addSubnode:_imageNode];
-  [self.view addSubview:_postNode.view];
+  [self.view addSubnode:_postNode];
 }