tweet 6.x-2.0

This release builds off of 1.7, but also requires that you run update.php if upgrading from the 1.x branch.

Changes:

- Tweaks to last commit to fix overlooked bugs
- Admin can now fully customize the Tweet text

As a result of the second general change, the API has changed (which is the reason for this new branch). Please see the documentation for the new API. To upgrade, simply change:

//$title is the title to use in the tweet, if any.
tweet_to_twitter($type, $title, $nid, $q);

to:

//$format is a string which indicates what text will appear in the tweet.
//[url] and [title] are replaced with the relevant URL and title, respectively.
//For example, "[url] [title] #hashtag" might output "http://example.com My Page Title #hashtag".
tweet_to_twitter($type, $format, $nid, $q);