Populate q_index in multi-thread encoding

This value needs to be copied to each thread's data structure.
This fixed artifact problem in multi-thread encoder.

Change-Id: Iab6d9745a1d44846aa503184705376f63a505597

vp8/encoder/ethreading.c

diff --git a/vp8/encoder/ethreading.c b/vp8/encoder/ethreading.c
index 557080d..8c49668 100644
--- a/vp8/encoder/ethreading.c
+++ b/vp8/encoder/ethreading.c
@@ -343,6 +343,9 @@
         z->block[i].zbin            = x->block[i].zbin;
         z->block[i].zrun_zbin_boost   = x->block[i].zrun_zbin_boost;
         z->block[i].round           = x->block[i].round;
+        z->q_index                  = x->q_index;
+        z->act_zbin_adj             = x->act_zbin_adj;
+        z->last_act_zbin_adj        = x->last_act_zbin_adj;
         /*
         z->block[i].src             = x->block[i].src;
         */

vp8/encoder/quantize.c

diff --git a/vp8/encoder/quantize.c b/vp8/encoder/quantize.c
index e57a264..3ca8758 100644
--- a/vp8/encoder/quantize.c
+++ b/vp8/encoder/quantize.c
@@ -609,6 +609,9 @@
 
     /* This initialization should be called at least once. Use ok_to_skip to
      * decide if it is ok to skip.
+     * Before encoding a frame, this function is always called with ok_to_skip
+     * =0, which means no skiping of calculations. The "last" values are
+     * initialized at that time.
      */
     if (!ok_to_skip || QIndex != x->q_index)
     {