**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.

if (!Array.isArray(expectedValues)) {
    warning(false, 'Invalid argument supplied to oneOf, expected an instance of array.');
    return emptyFunction.thatReturnsNull;
  }
  function validate(props, propName, componentName, location, propFullName) {
    var propValue = props[propName];
    for (var i = 0; i < expectedValues.length; i++) {
      if (is(propValue, expectedValues[i])) {
        return null;
      }
    }
    var locationName = ReactPropTypeLocationNames[location];
    var valuesString = JSON.stringify(expectedValues);
    return new Error(
      `Invalid ${locationName} \`${propFullName}\` of value \`${propValue}\` ` +
      `supplied to \`${componentName}\`, expected one of ${valuesString}.`
    );
  }
  return createChainableTypeChecker(validate);
}
function createObjectOfTypeChecker(typeChecker) {
  function validate(props, propName, componentName, location, propFullName) {
    if (typeof typeChecker !== 'function') {
      return new Error(
        `Property \`${propFullName}\` of component \`${componentName}\` has invalid PropType notation inside objectOf.`
      );