Add more tests for IDBCursor advance
Improve and rename tests for IDBCursor advance

 - duplicate file name.
Improve tests for IDBCursor advance

 - split checkpoint into its own file.
Use setup() in DOM tests that use constants.js.
Improve the ChildNode.remove() tests to always run the same number of tests.
Merge pull request #925 from Ms2ger/improve-test-structure

Use setup() more in DOM tests
Moved code
Update to latest testharness.js
Merge pull request #826 from yunxiaoxie/yunxiaoxie/idbcursor-advance

Add more tests for IDBCursor advance