[test] Add pixelmatch; use in annotation tests

scripts/linux/after_script.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+
+set -e
+set -o pipefail
+
+if [ ! -z "${AWS_ACCESS_KEY_ID}" ] && [ ! -z "${AWS_SECRET_ACCESS_KEY}" ] ; then
+    # Install and add awscli to PATH for uploading the results
+    pip install --user awscli
+    export PATH="`python -m site --user-base`/bin:${PATH}"
+
+    REPO_NAME=$(basename $TRAVIS_REPO_SLUG)
+
+    aws s3 cp --recursive --acl public-read test/fixtures/annotations \
+        s3://mapbox/$REPO_NAME/render-tests/$TRAVIS_JOB_NUMBER/annotations
+fi

scripts/linux/configure.sh

@@ -15,6 +15,7 @@ GEOJSONVT_VERSION=2.1.6.3
 VARIANT_VERSION=1.0
 RAPIDJSON_VERSION=1.0.2
 GTEST_VERSION=1.7.0
+PIXELMATCH_VERSION=0.9.0
 
 function print_opengl_flags {
     CONFIG+="    'opengl_cflags%': $(quote_flags $(pkg-config gl x11 --cflags)),"$LN