Split out some assertions in the Node#cloneNode tests.
Only test Element members for Elements.
Add some additional tests.
Add a test for cloneNode with a prefix.
Update the help URL.
Add a test for Node#cloneNode on a non-HTML element.
Use assert_not_equals.
Give the Node#cloneNode tests names.
Merge pull request #1326 from Ms2ger/clone-prefix

Extend the Node#cloneNode test.