Merge changes Icfc16070,Ied47a248,I8af087d9,I322a1366,If04580af into nextgenv2
* changes: Palette: Use inverse_color_order to find color index faster. Rewrite some loops to avoid -Wunsafe-loop-optimizations warnings. Remove some useless casts Add compiler warning flag -Wextra and fix related warnings. Declare some array sizes to be constants (known at compile time).