Check for share type when choosing favorite items.
Use the com.instagram.exclusivegram UTI for Instagram.

More info: http://instagram.com/developer/iphone-hooks/
Relevant section: "Alternatively, if you want to show only Instagram in the application list (instead of Instagram plus any other public/jpeg-conforming apps) you can specify the extension class igo, which is of type com.instagram.exclusivegram."
Revert "Check for share type when choosing favorite items."

This reverts commit fbf480cf38750d9d5d861c7f46ab52d0db4cbb3d.
Determining Instagram availability inside canShare. 
Merge pull request #633 from matej/instagram-fixes

Instagram fixes
Fix regression from d01be018f6, do not override existing status.
Merge pull request #636 from Javache/fix-twitter-urls

Fix regression in classic Twitter sharer, do not override existing status.