Fix discussion page's "limit", "after", "before", "count" params.

This pull request fixes the bug that causes discussion (for links and wikis) pages's `limit`, `after`, `before`, `count` parameter to not work at all.

**Examples**

For a link, the following URLs all show the same results:

- http://www.reddit.com/r/funny/duplicates/1aw7s5/
- http://www.reddit.com/r/funny/duplicates/1aw7s5/?limit=1
- http://www.reddit.com/r/funny/duplicates/1aw7s5/?after=t3_162prl

For a wiki, the following URLs all show the same results:

- http://www.reddit.com/wiki/discussions/reddiquette
- http://www.reddit.com/wiki/discussions/reddiquette?limit=1
- http://www.reddit.com/wiki/discussions/reddiquette?after=t3_1csk1m

Also, normally, the `limit` param is capped by `VLimit` at 100. This bug causes pages like http://www.reddit.com/r/funny/duplicates/1aw7s5/ to list more than 100 results per request.