Merge changes I341bd674,Ia9a0d71d,I71c1f906,I2e36e07c,I94ee2e85, ...

* changes:
  Refactor check_initial_width
  Move noise_sensitivity to set_encoder_config
  Remove extra function calls in check_initial_width
  Move init_ref_frame_bufs to vp9_create_compressor
  Remove bits_left update in encoder_encode()
  Add vp9_get_encoder_config / vp9_get_frame_info
  vp9_get_coding_frame_num()
  Make [min/max]_gf_interval static under rate_ctrl
  Add rate_ctrl flag