Added some extra checks for checking the undo/redo logs
Better tests for undo/redo buffers
Fixed a test (it was 'redo' in the test, should have been 'undo')
Added some more undo-buffer tests
Got rid of assert_node() since it was basically identical to assert_hash()
Fixed a bug in a test - set the wrong value when creating the first node
Fixed another test bug - was checking the wrong addresses to see what  node returned
Fixed the same bug again - checking the wrong addresses - in another place
Fixed a bug in a test that was looking for the wrong number of nodes
Add some better length checks, since assert_hash() doesn't check the length