Merge pull request #4007 from pchote/fixes

Fix playtest breakages.
Palette header comes *after* the frame. Fixes #3728.
Add Subtractive blend mode for d2k move-flash.
Fieldloader support for longs.
Add PaletteFromR8 for loading embedded palettes.

The frames that define a custom palette are:
Frame range ->  offset (mem offset)
         38 ->   12007 (22063136)
        178 ->  159947 (21859680)
3494 - 3501 -> 2437846 (23366680)
3502 - 3509 -> 2443858 (23422744)
3510 - 3511 -> 2459105 (23363608)
3621 - 3625 -> 2572352 (23550488)
3739 - 3742 -> 2676956 (23534796)