Checkpoint 2:
gfxdecode devices must now be assigned a palette in MCFG. Added palette devices to several MESS drivers and devices to comply with this requirement. This palette is assigned as a default to the gfx_elements created by the device (but still not used for drawing yet, except in the UI graphics viewer)

Tilemaps now have a pointer to a palette device and use that palette for rgb32 drawing, rather than the palette of the screen or bitmap they are drawing to (since rgb32 screens don't have palettes now). When a tilemap is created, it takes its palette from the gfxdecode device it was created with, but you can change a tilemap's palette device with set_palette() at any time (doing this does not mark the tilemap dirty, since all tilemaps use indexed bitmaps internally)