Merge changes Icd1a2a5a,I204d17a1,I3ed92117 into experimental

* changes:
  Initial support for resolution changes on P-frames
  Avoid allocating memory when resizing frames
  Adds a test for the VP8E_SET_SCALEMODE control

diff --cc vp9/decoder/vp9_decodframe.c
Simple merge

diff --cc vp9/encoder/vp9_bitstream.c
Simple merge

diff --cc vp9/encoder/vp9_onyx_if.c
Simple merge

diff --cc vp9/encoder/vp9_onyx_int.h
Simple merge

diff --cc vp9/encoder/vp9_rdopt.c
Simple merge

diff --cc vp9/vp9_cx_iface.c
Simple merge