Fix incompatibility between two experiments

ext_tile is not compatible with reference_buffer, this commit changes
to disable refrence_buffer when ext_tile is enabled.

BUG=aomedia:114

Change-Id: I6416f4c731bec1c4cfeab3cdb539f359627ed2e2

configure

diff --git a/configure b/configure
index 4438841..70a66d7 100755
--- a/configure
+++ b/configure
@@ -479,6 +479,11 @@
     enabled ec_multisymbol && ! enabled ans && soft_enable daala_ec
     enabled ec_multisymbol && ! enabled daala_ec && soft_enable ans
     enabled daala_ec && enable_feature ec_multisymbol
+    if enabled ext_tile; then
+      log_echo "ext_tile not compatible with reference_buffer, so"
+      log_echo "disabling reference_buffer"
+      disable_feature reference_buffer
+    fi
     if enabled global_motion && (enabled ext_inter || enabled dual_filter); then
       log_echo "global_motion currently not compatible with ext_inter"
       log_echo "and dual_filter. Disabling global_motion."