Re-implementation of hotlist via general tree code. Animations can be stopped once more. Purged a few xcalloc() calls.
svn path=/import/netsurf/; revision=1394
Fix for recent GIF decoding bug. Rectangular pixel mode-friendly sprites for hotlist. Slight change to history image size to please Tinct. Support for foreground and background image quality settings. Support for error diffusion and bi-linear filtering (Tinct still requires some further work)
svn path=/import/netsurf/; revision=1336