Add a a warning to Blob-constructor.html.
Test null and undefined as the Audio constructor argument

Per WebIDL, an undefined optional argument should be treated as a
missing argument. Also test null for extra paranoia.
Remove tests obsoleted by 2d.gradient.object.invalidcolour.html.
Merge BlobBuilder.html into historical.html.
Merge pull request #527 from Ms2ger/warn-sequence-Blob

Add a a warning to Blob-constructor.html.
Merge pull request #537 from Ms2ger/addColorStop

Remove tests obsoleted by 2d.gradient.object.invalidcolour.html.
Merge pull request #538 from Ms2ger/BlobBuilder

Merge BlobBuilder.html into historical.html.
Merge pull request #531 from foolip/audio-null-undefined

Test null and undefined as the Audio constructor argument