comments: remove rule that you can't upvote your own comments.

Remove this rule for several reasons:

* A single upvote usually isn't enough to matter, especially with the
  new comment threshold.
* It felt weird that trying to vote on a comment could fail.
* Disabling the upvote button on your own comments feels weird.
* Most other sites allow you to upvote your own comments.
* You're allowed to upvote your own uploads, so it doesn't make sense
  that you can't upvote your own comments.

CHANGELOG.md

@@ -33,6 +33,8 @@
 * The maximum comment threshold is now 5 and the minumum threshold is now
   -100. You can't set your threshold any higher or lower than this.
 
+* Removed the rule that you can't upvote your own comments.
+
 * Changed the way [quote] tags look. Now quotes are Reddit-style instead of
   traditional forum style.