In response to rmckillen’s post re: bit.ly and servers not allowing file_get_contents() I have spent the last few hours coming up with this to get around that.
Replace
$url = apply_filters('tweet_blog_post_url', get_permalink($post_id));
with
$ch = curl_init("https://api.bit.ly/shorten?format=xml;version=2.0.1&login=USERNAME&apiKey=APIKEY&longUrl=".get_permalink($post_id));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HEADER, 0);
$data = curl_exec($ch);
curl_close($ch);
$xml = new SimpleXmlElement($data, LIBXML_NOCDATA);
$bitly = $xml->results->nodeKeyVal->shortUrl;
$url = apply_filters('tweet_blog_post_url', $bitly);
Hope that helps anyone that needs it.