Validate DCO on Travis

Copied straight from Docker, replacing github.com/docker/docker
with github.com/docker/fig in .validate.

Signed-off-by: Ben Firshman <ben@firshman.co.uk>

script/.validate

@@ -0,0 +1,33 @@
+#!/bin/bash
+
+if [ -z "$VALIDATE_UPSTREAM" ]; then
+	# this is kind of an expensive check, so let's not do this twice if we
+	# are running more than one validate bundlescript
+	
+	VALIDATE_REPO='https://github.com/docker/fig.git'
+	VALIDATE_BRANCH='master'
+	
+	if [ "$TRAVIS" = 'true' -a "$TRAVIS_PULL_REQUEST" != 'false' ]; then
+		VALIDATE_REPO="https://github.com/${TRAVIS_REPO_SLUG}.git"
+		VALIDATE_BRANCH="${TRAVIS_BRANCH}"
+	fi
+	
+	VALIDATE_HEAD="$(git rev-parse --verify HEAD)"
+	
+	git fetch -q "$VALIDATE_REPO" "refs/heads/$VALIDATE_BRANCH"
+	VALIDATE_UPSTREAM="$(git rev-parse --verify FETCH_HEAD)"
+	
+	VALIDATE_COMMIT_LOG="$VALIDATE_UPSTREAM..$VALIDATE_HEAD"
+	VALIDATE_COMMIT_DIFF="$VALIDATE_UPSTREAM...$VALIDATE_HEAD"
+	
+	validate_diff() {
+		if [ "$VALIDATE_UPSTREAM" != "$VALIDATE_HEAD" ]; then
+			git diff "$VALIDATE_COMMIT_DIFF" "$@"
+		fi
+	}
+	validate_log() {
+		if [ "$VALIDATE_UPSTREAM" != "$VALIDATE_HEAD" ]; then
+			git log "$VALIDATE_COMMIT_LOG" "$@"
+		fi
+	}
+fi