breaking(Transition): Only call findDOMNode if necessary (#2)

Cherry-picking reactjs#468

## Breaking
Callbacks that use argument spread or access `arguments` will not have acces to the DOM node. The DOM node is only passed if Function.prototype.length is greater than 0.

```
// no node passed
const noNodeCallback = () => {};
// node passed
const withNodeCallback = node => {};
```

The first callback enables strict mode compatible usage of `Transition`. If you expect the node in callbacks a call to `findDOMNode` is required which issues a warning in `React.StrictMode`.

Author: eps1lon

src/Transition.js

@@ -208,7 +208,7 @@ class Transition extends React.Component {
     if (nextStatus !== null) {
       // nextStatus will always be ENTERING or EXITING.
       this.cancelNextCallback()
-      const node = ReactDOM.findDOMNode(this)
+      const node = this.needsNode() ? ReactDOM.findDOMNode(this) : null;
 
       if (nextStatus === ENTERING) {
         this.performEnter(node, mounting)
@@ -312,7 +312,7 @@ class Transition extends React.Component {
     this.setNextCallback(handler)
 
     const doesNotHaveTimeoutOrListener = timeout == null && !this.props.addEndListener
-    if (!node || doesNotHaveTimeoutOrListener) {
+    if (doesNotHaveTimeoutOrListener) {
       setTimeout(this.nextCallback, 0)
       return
     }
@@ -326,6 +326,19 @@ class Transition extends React.Component {
     }
   }
 
+  needsNode() {
+    return [
+      'addEndListener',
+      'onEnter',
+      'onEntering',
+      'onEntered',
+      'onExit'
+    ].some(callbackName => {
+      const callback = this.props[callbackName];
+      return callback && callback.length > 0
+    })
+  }
+
   render() {
     const status = this.state.status
     if (status === UNMOUNTED) {