Implement Comparable in PersistentList

Patch for this issue; done with Jeroen van Dijk and Razvan Petruescu at a clojure meetup. Any feedback welcome; the learning for me here is not the fix, but learning how to deal with ant and jira etc.

Looks like you have navigated the steps for creating a patch in the desired format, and attaching it to a JIRA ticket, just fine. I see your name on the list of contributors, which is a precondition before a patch can be committed to Clojure or a contrib library.

You've gotten past what are actually the easier parts. There is still the issue of whether this ticket is even considered by the Clojure core team to be an enhancement worth making a change to Clojure. Take a look at the JIRA workflow here if you haven't seen it already and are curious: http://dev.clojure.org/display/community/JIRA+workflow

If you like Pascal think that this is a change you really want to see in Clojure, you may vote on this or any other JIRA ticket (except ones you create yourself – the creator is effectively the 0th voter for a ticket). Log in and click on the Vote link near the top right, and/or Watch to get email updates of changes.

Andy, thanks for the info. I was not aware of the JIRA workflow.

It seems like other sequences besides PersistentLists should be comparable, one obvious example is `clojure.lang.APersistentVector$RSeq`. I stumbled upon it not being Comparable when trying to rewrite `(sort-by (juxt val key) m)` as `(sort-by rseq m)`