Split up interfaceCheck.
Split up runInvalidSelectorTest.
Split up the Selectors API level 2 tests.
Only run the relevant tests in the new matches and find/findAll tests.
Remove testType arguments.
Split out matches-specific code from level2-lib.js.
Split out find/findAll-specific code from level2-lib.js.
Make traverse work if the root is not an Element.

In particular, this is done in some of the runSpecialSelectorTests calls.
Use |var| rather than |let| in Document-getElementById.html.

This snuck in while porting a Servo test.
Slightly extend the Document#createAttribute test.
Split out the guts of Document-createComment.html.
Add a test for Document#createTextNode.
Split out the guts of Comment-constructor.html.
Add a test for the Text constructor.
Test that DOMImplementation#createDocument returns an XML document as tested by Document#createElement.
Merge pull request #1393 from Ms2ger/createDocument-htmldocument

Test that DOMImplementation#createDocument returns an XML document...
Merge pull request #1391 from Ms2ger/createAttribute

Slightly extend the Document#createAttribute test.
Merge pull request #1390 from Ms2ger/getElementById

Use |var| rather than |let| in Document-getElementById.html.
Merge pull request #1392 from Ms2ger/Text-constructor

Add a test for the Text constructor.
Merge pull request #1389 from Ms2ger/createTextNode

Add a test for Document#createTextNode.