Fixed typo for __ne__

We could probably also refactor `__ne__` to call `__eq__`
Merge pull request #208 from shuhaowu/typo-fixes

Fixed typo for __ne__
Getting rid of RiakLink in favour of tuples

Please review this carefully! There are some potential issues that we
need to address. Before that, some points needs to be noted:

 1. `RiakLink.get` was actually never tested in code.
 2. The new interface should be easier to use in a lot of scenarios
    where you are iterating through links (you can do
    `for bucket, key, tag in obj.get_links()`), it maybe less clear than
    a class. IMO this is not the case as a 3-item tuple is sufficient,
    but if the `RiakLink.get` method is actually used a lot in the wild,
    it might be benificial to include some sort of wrapper function.

A potential issue that I identified: I've noted that `client.index`
doesn't actually perform the Riak 2i operation as specified in the HTTP
and PBC protocal and does a map reduce operation instead. Right now an
index operation actually seems to return links, which seems weird (see
line 110 in riak/test/test_2i.py) as it seems like the Riak API just
returns keys and this is returning `(bucket, key, None)`
Added a namedtuple convenience class for links

Backend code do not need to change. The user is free to use RiakLink or
a 3-item tuple.
Fix some bucket-related breakages.
Bunch of pep8 and pyflakes fixes.