react 15.3.0

Add React.PureComponent - a new base class to extend, replacing react-addons-pure-render-mixin now that mixins don't work with ES2015 classes. (@spicyj in #7195)
Add new warning when modifying this.props.children. (@jimfb in #7001)
Fixed issue with ref resolution order. (@gaearon in #7101)
Warn when mixin is undefined. (@swaroopsm in #6158)
Downgrade "unexpected batch number" invariant to a warning. (@spicyj in #7133)
Validate arguments to oneOf and oneOfType PropTypes sooner. (@troydemonbreun in #6316)
Warn when calling PropTypes directly. (@Aweary in #7132, #7194)
Improve warning when using Maps as children. (@keyanzhang in #7260)
Add additional type information to the PropTypes.element warning. (@alexzherdev in #7319)
Improve component identification in no-op setState warning. (@keyanzhang in #7326)

Fix issue with nested server rendering. (@Aweary in #7033)
Add xmlns, xmlnsXlink to supported SVG attributes. (@salzhrani in #6471)
Add referrerPolicy to supported HTML attributes. (@Aweary in #7274)
Fix issue resulting in <input type="range"> initial value being rounded. (@troydemonbreun in #7251)

Initial public release of package allowing more focused testing. Install with npm install react-test-renderer. (@spicyj in #6944, #7258, @iamdustan in #7362)

Fix issue resulting in excessive warnings when encountering an internal measurement error. (@sassanh in #7299)

Implement type property on for events created via TestUtils.Simulate.*. (@yaycmyk in #6154)
Fix crash when running TestUtils with the production build of React. (@gaearon in #7246)