react 15.2.0

Add error codes to production invariants, with links to the view the full error text. (@keyanzhang in #6948)
Include component stack information in PropType validation warnings. (@spicyj in #6771)
Include component stack information in key warnings. (@keyanzhang in #6799)
Stop validating props at mount time, only validate at element creation. (@keyanzhang in #6823)
New invariant providing actionable error in missing instance case. (@yungsters in #6990)
Add React.PropTypes.symbol to support ES2015 Symbols as props. (@puradox in #6377)
Fix incorrect coercion of ref or key that are undefined in development (@gaearon in #6880)
Fix a false positive when passing other element’s props to cloneElement (@ericmatthys in #6268)

Add warning for unknown properties on DOM elements. (@jimfb in #6800, @gm758 in #7152)
Properly remove attributes from custom elements. (@grassator in #6748)
Fix invalid unicode escape in attribute name regular expression. (@nbjahan in #6772)
Add onLoad handling to <link> element. (@roderickhsiao in #6815)
Add onError handling to <source> element. (@wadahiro in #6941)
Handle value and defaultValue more accurately in the DOM. (@jimfb in #6406)
Fix events issue in environments with mutated Object.prototype. (@Weizenlol in #6886)
Fix issue where is="null" ended up in the DOM in Firefox. (@darobin in #6896)
Improved performance of text escaping by using escape-html. (@aickin in #6862)
Fix issue with dangerouslySetInnerHTML and SVG in Internet Explorer. (@joshhunt in #6982)
Fix issue with <textarea> placeholders. (@jimfb in #7002)
Fix controlled vs uncontrolled detection of <input type="radio"/>. (@jimfb in #7003)
Improve performance of updating text content. (@trueadm in #7005)
Ensure controlled <select> components behave the same on initial render as they do on updates. (@yiminghe in #5362)

Add isRunning() API. (@nfcampos in #6763)
Improve accuracy of lifecycle hook timing. (@gaearon in #6858)
Fix internal errors when using ReactPerf with portal components. (@gaearon in #6860)
Fix performance regression. (@spicyj in #6770)
Add warning that ReactPerf is not enabled in production. (@sashashakun in #6884)

Dependencies on React Native modules use CommonJS requires instead of providesModule. (@davidaurelio in #6715)