vp9: add fate tests for show-existing-frame feature.

Samples available at:
http://downloads.webmproject.org/test_data/libvpx/vp90-2-10-show-existing-frame.webm
http://downloads.webmproject.org/test_data/libvpx/vp90-2-10-show-existing-frame2.webmSigned-off-by: Michael Niedermayer <michaelni@gmx.at>

tests/fate/vpx.mak

@@ -101,6 +101,8 @@ $(foreach W,$(VP9_SIZE_B),$(eval $(foreach H,$(VP9_SIZE_B),$(eval $(call FATE_VP
 $(eval $(call FATE_VP9_SUITE,03-deltaq,$(1),$(2)))
 $(eval $(call FATE_VP9_SUITE,06-bilinear,$(1),$(2)))
 $(eval $(call FATE_VP9_SUITE,09-lf_deltas,$(1),$(2)))
+$(eval $(call FATE_VP9_SUITE,10-show-existing-frame,$(1),$(2)))
+$(eval $(call FATE_VP9_SUITE,10-show-existing-frame2,$(1),$(2)))
 $(eval $(call FATE_VP9_SUITE,2pass-akiyo,$(1),$(2)))
 $(eval $(call FATE_VP9_SUITE,parallelmode-akiyo,$(1),$(2)))
 $(eval $(call FATE_VP9_SUITE,segmentation-aq-akiyo,$(1),$(2)))

tests/ref/fate/vp9-10-show-existing-frame

+#format: frame checksums
+#version: 1
+#hash: MD5
+#tb 0: 1/30
+#stream#, dts,        pts, duration,     size, hash
+0,          0,          0,        1,   152064, 18981342ec178e082519451062c3a67f
+0,          1,          1,        1,   152064, 04ab9dbeac49ec31be58f6e671698e05
+0,          6,          6,        1,   152064, a41f00034923e56ba51a0b598acc2e3a
+0,          7,          7,        1,   152064, 63fa55ae9535ccdf06d44cce8065dda6
+0,          9,          9,        1,   152064, 0e4b08e14d919edee2bbff2ecd47de57
+0,         10,         10,        1,   152064, 0e4b08e14d919edee2bbff2ecd47de57
+0,         13,         13,        1,   152064, 9e932915c67a789f6877e6d3f76d3649
+0,         14,         14,        1,   152064, 12f2e975c217e7ffcf334524e8acec35
+0,         15,         15,        1,   152064, 9e932915c67a789f6877e6d3f76d3649

tests/ref/fate/vp9-10-show-existing-frame2

+#format: frame checksums
+#version: 1
+#hash: MD5
+#tb 0: 1/30
+#stream#, dts,        pts, duration,     size, hash
+0,          0,          0,        1,   152064, 382b12c33cd86b38758706b8ebca8a85
+0,          1,          1,        1,   152064, 799544370b35c91711a5b49a28cf86a8
+0,          2,          2,        1,   152064, 7218eb4b6d1c7aea4f96ee47ad675e8e
+0,          3,          3,        1,   152064, 627466200370e6ad60ea570d31be66e3
+0,          4,          4,        1,   152064, 7dc65a2af108379f2b9265a9a1ea7cf8
+0,          5,          5,        1,   152064, c979e2f084760775a567f60f79f28198
+0,          6,          6,        1,   152064, fe668a6417aa0543e4ed4d1c67c5cbcb
+0,          7,          7,        1,   152064, bf9901e39815fa93cce0ed5b02b2ef2d
+0,          8,          8,        1,   152064, 627466200370e6ad60ea570d31be66e3
+0,          9,          9,        1,   152064, 7dc65a2af108379f2b9265a9a1ea7cf8
+0,         10,         10,        1,   152064, c979e2f084760775a567f60f79f28198
+0,         11,         11,        1,   152064, fe668a6417aa0543e4ed4d1c67c5cbcb
+0,         13,         13,        1,   152064, 627466200370e6ad60ea570d31be66e3
+0,         14,         14,        1,   152064, 7dc65a2af108379f2b9265a9a1ea7cf8
+0,         15,         15,        1,   152064, c979e2f084760775a567f60f79f28198