**Do you want to request a _feature_ or report a _bug_?**
Enhancement

**What is the current behavior?**
Element type checker is not as informative as the other ones.

**What is the expected behavior?**
It would be nice to provide the actual type of the prop passed similarly to other type checkers. I.e., instead of 

> Invalid prop `Prop` supplied to `Component`, expected a single ReactElement.

say

> Invalid prop `Prop` of type `type` supplied to `Component`, expected a single ReactElement.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**
Seeing this on 15.2.1 but I think it's also applicable to previous versions.

I know the general intention is to move away from prop types, but if there isn't a specific reason for the current behavior I can look into making this more pretty.

function isNode(propValue) {
  switch (typeof propValue) {
    case 'number':
    case 'string':
    case 'undefined':
      return true;
    case 'boolean':
      return !propValue;
    case 'object':
      if (Array.isArray(propValue)) {
        return propValue.every(isNode);
      }
      if (propValue === null || ReactElement.isValidElement(propValue)) {
        return true;
      }
      var iteratorFn = getIteratorFn(propValue);
      if (iteratorFn) {
        var iterator = iteratorFn.call(propValue);
        var step;
        if (iteratorFn !== propValue.entries) {
          while (!(step = iterator.next()).done) {
            if (!isNode(step.value)) {
              return false;
            }
          }
        } else {
          
          while (!(step = iterator.next()).done) {
            var entry = step.value;
            if (entry) {