Closure fix; force cast from Element to Node.
Closure tweak: variable 'd' declared twice within the same method.
Closurize dygraph-options.js. Not done.

Also fix bug: this.labels_ was never used! Booo...
Closure fix type Dyraph->Dygraph.
Closurize rgbcolor.js
Some closurifying dygraph-canvas and dygraph-layout.
Merge branch 'master' of github.com:danvk/dygraphs into closure

Conflicts:
	dygraph-options.js
Reponses to code review for https://github.com/danvk/dygraphs/pull/237
Follow-on to pull request 237, closurifying some code.
Merge pull request #237 from kberg/closure

Fix closure bugs in Dygraphs