For review: gdk-pixbuf: GIF loader memory usage fix

[Денис Паук <pauk denis gmail com>]

Hi!

Could  you please review my change for bug
https://bugzilla.gnome.org/show_bug.cgi?id=585425 (GIF loader uses about 280M of VmRSS for a 200Kb GIF).

I made such changes:
1. added use same previous pixbuf for new frame, with set NULL to previous frame link
2. added function for clean up all pixbuf caches in animation list, such caches cant be accessed directly and we restore composed pixbuf on request.

If i missed something, please write.

Thank you!  
 

--
Best regards,
                  Denis.