Merge changes I3922dea2,I3bab2848,I21f7478a,Ida5de713,Ib9f0eefe, ... into nextgenv2

* changes:
  Fix warnings reported by -Wshadow: Part4: main directory
  Fix warnings reported by -Wshadow: Part3: test/ directory
  Fix warnings reported by -Wshadow: Part2b: more from av1 directory
  Fix warnings reported by -Wshadow: Part2: av1 directory
  Fix warnings reported by -Wshadow: Part1b: scan_order struct and variable
  Fix warnings reported by -Wshadow: Part1: aom_dsp directory
  Move STAT_TYPE enum to source file.
  Code cleanup: mainly rd_pick_partition and methods called from there.