**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.

spyOn(console, 'error');
      PropTypes.oneOf('red', 'blue');
      expect(console.error).toHaveBeenCalled();
      expect(console.error.calls.argsFor(0)[0])
        .toContain('Invalid argument supplied to oneOf, expected an instance of array.');
      typeCheckPass(PropTypes.oneOf('red', 'blue'), 'red');
    });
    it('should warn for invalid values', function() {
      typeCheckFail(
        PropTypes.oneOf(['red', 'blue']),
        true,
        'Invalid prop `testProp` of value `true` supplied to ' +
        '`testComponent`, expected one of ["red","blue"].'
      );
      typeCheckFail(
        PropTypes.oneOf(['red', 'blue']),
        [],
        'Invalid prop `testProp` of value `` supplied to `testComponent`, ' +
        'expected one of ["red","blue"].'
      );
      typeCheckFail(
        PropTypes.oneOf(['red', 'blue']),
        '',
        'Invalid prop `testProp` of value `` supplied to `testComponent`, ' +
        'expected one of ["red","blue"].'
      );
      typeCheckFail(
        PropTypes.oneOf([0, 'false']),
        false,
        'Invalid prop `testProp` of value `false` supplied to ' +