Remove several dead functions
Content-aware resize: fixed 32bpp issues, added serpentine scanning

Serpentine scanning is awesome, because it allows images on uniform
backgrounds (where both sides of an object of interest have identical
energy maps) to lose or gain seams equally on the left and right.

Without this change, seams would be preferentially moved from
left-to-right, so an image like
http://en.wikipedia.org/wiki/Blue_marble#mediaviewer/File:North_America_from_low_orbiting_satellite_Suomi_NPP.jpg
would see its left side chopped to a minimal amount before any seams
disappeared from the right.

Still to-do is an attempt to make this work with layers, so I can add it
back to the Image menu.