Don't add the reference element to the parent node if there is none.

If added to a parent, ensure it is still actually removed when an error
occurs.
Remove bit-rotted web-animations-visualization
Remove bit-rotted web-animations-test
Merge pull request #268 from dstockwell/remove-vis

Remove bit-rotted web-animations-visualization
Merge pull request #269 from dstockwell/remove-test

Remove bit-rotted web-animations-test
Add new test to testcases.js
Rename testharness_bootstrap.js to bootstrap.js
Update reference to bootstrap.js in testcases
Load web-animations.js in bootstrap
Remove web-animations.js script from testcases
Add a nopolyfill flag to allow manual loading of the polyfill
Remove calls to console.log from test-runner and testharness_timing
Reimplement nochecks flag to toggle loading of '-checks.js' files
Specify nochecks flag for tests with no -checks.js file
Stop trying to post results once post failures are detected
Load polyfill directly in manual tests
Stop exporting StepTimingFunction and SplineTimingFunction
Add placeholders for missing interfaces
Merge pull request #266 from dstockwell/update-state

Don't add the reference element to an absent parent
Merge pull request #275 from dstockwell/remove-step-timing

Stop exporting StepTimingFunction and SplineTimingFunction