Change it from transparent white to transparent black, which matches
the transparent color assumed in Webp dispose-to-background method.
Also pre-multiply background colors before comparison in anim_diff,
just as what is done with regular pixel values.
Change-Id: I5a790522df21619c666ce499f73e42294ed276f2
+ jenkins fixes for native config (library order)
+ add a missing -lm
+ replace log10 by log, just in case
+ partially reverted configure.ac to remove the C++ part
Change-Id: Iee099c544451b23c6cfaca53d5a95d2d332e066e
