**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.

var props = {testProp: value};
  var error = declaration(
    props,
    'testProp',
    'testComponent',
    ReactPropTypeLocations.prop,
    null,
    ReactPropTypesSecret
  );
  expect(error instanceof Error).toBe(true);
  expect(error.message).toBe(message);
}
function typeCheckPass(declaration, value) {
  var props = {testProp: value};
  var error = declaration(
    props,
    'testProp',
    'testComponent',
    ReactPropTypeLocations.prop,
    null,
    ReactPropTypesSecret
  );
  expect(error).toBe(null);
}
function expectWarningInDevelopment(declaration, value) {