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).

diff --cc aomenc.c
Simple merge

diff --cc av1/common/entropymode.h
Simple merge

diff --cc av1/encoder/encoder.c
Simple merge

diff --cc av1/encoder/rdopt.c
Simple merge

diff --cc av1/encoder/tokenize.c
Simple merge

diff --cc configure
Simple merge