About sina weibo in China, They didn't return the :callback_confirmed when we get request token,
But is also need to varify the :oauth_verifier params at call back phase， so I made this patch so I can define it outside in the strategies.
Sina weibo does not returned :callback_confirmed params so make it ca…
…n defined in strategies.
This patch would also help with a project in our university with a similar situation. Is it going to be merged?