Only allow edited tiddlers to show up once

Currently if a tiddler is saved regularly during editing then this tiddler is display multiple times in the list.
Would be more useful if only the last time it was saved is shown

The issue is particularly apparent when a use is using an editing SPA, such /edit, that auto saves regularly. This can lead to the whole stream of edits referring to the same tiddler repeeatedly. See image
![tapas_repeating_tids](https://f.cloud.github.com/assets/299875/605457/0fa697da-cd17-11e2-8924-c294510a4859.png)