Checking in vendor folder for ease of using go get.

vendor/git.apache.org/thrift.git/build/docker/check_unmodified.sh

@@ -0,0 +1,42 @@
+#!/bin/bash
+#
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements. See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership. The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License. You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied. See the License for the
+# specific language governing permissions and limitations
+# under the License.
+#
+
+# Download prebuilt docker image and compare Dockerfile hash values
+
+set -ex
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+DISTRO=$1
+SRC_IMG=thrift/thrift-build:$DISTRO
+
+function try_pull {
+  docker pull $SRC_IMG
+  cd ${SCRIPT_DIR}/$DISTRO
+  docker run $SRC_IMG bash -c 'cd .. && sha512sum Dockerfile' > .Dockerfile.sha512
+  sha512sum -c .Dockerfile.sha512
+}
+
+if try_pull; then
+  echo Dockerfile seems identical. No need to rebuild from scratch.
+  docker tag thrift/thrift-build:$DISTRO thrift-build:$DISTRO
+else
+  echo Either Dockerfile has changed or pull failure. Need to build brand new one.
+  exit 1
+fi