Copy instance data when copying block instances

Because no blocks implement the interface we are adding, we will need to hack an existing block. We will use the HTML block.

Success case

1. (hack) Add the following function to the HTML block (blocks/html/block_html.php):

   function instance_copy($fromid) {

   return true;

   }

2. Login as admin. Go to "Home / ▶ Site administration / ▶ Appearance / ▶ Default Dashboard page" and click "Blocks editing on"
3. Add a HTML block to page. Add some content to the block.
4. Click "Blocks editing off" and click "Dashboard" to take you to the Dashboard page.
5. Click "Customise this page" then "Reset page to default" and observe that a) there are no errors on the page, and b) the HTML block that you added displays fine (i.e. the content is there).
6. Before continuing to the next test, click "Reset page to default".

Fail case

1. (hack) Change the function you added in the first success case test in blocks/html/block_html.php to be:

   function instance_copy($fromid) {

   return false;

   }

2. Assuming you are still logged in as admin from the previous test, go to the Dashboard page and click "Customise this page" and "Reset page to default".
3. Observe that there should now be a developer debug error indicating the block instance id's that were attempted to be copied and that block-specific data was unable to be copied.