Support two-way binding for checkboxes in LinkedValueMixin via 'checkedLink' property
Add invariant if both checkedLink and valueLink are provided
Fix typo in ReactDOMInput-test
Fix comparison in _handleLinkedCheckChange
Use Simulate.click instead of Simulate.input for simulating input on
checkbox.
Merge pull request #880 from jbaiter/reactlink_checkbox

Support two-way binding for checkboxes in LinkedValueMixin via 'checkedLink' property