LICE_gif_write: fixed transparency for partial updates, oops -- from e3256229
LICE_gif_write: improved auto-transparency logic -- from 921418d8
lice_gif_write: properly support variable alpha threshold for caller-alpha, also support mask in auto-transparency mode by using low 8 bits of transalpha as mask -- from 95749e6d
lice_gif_write: if transalpha has 0x100 cleared, don't use fancy new statistics to decide whether or not to use transparency -- from a912e96f