Tightened up constants and methods tests so that the addition of any unknown properties or functions will cause the tests to fail. This change will require these tests to be updated if future versions of the spec are released which add new properties to the WebGLRenderingContext, but the current situation where implementations may accidentally expose properties without failing these tests is unworkable.
Merge pull request #249 from kenrussell/functions-and-properties

Tightened up constants and methods tests so that the addition of any unk...