bug 19646 Localization of img_auth.php - with enhancements
https://bugzilla.wikimedia.org/show_bug.cgi?id=19646

1. Localize img_auth.php using core messages
2. Reorder checks to make sense (and eliminate redundancy)n
3. Add hook 'ImgAuthBeforeStream' to allow custom checking
4. Add globals wgImgAuthDetails,
5. Move all "wfDebugLog" into the rejection functions