Add OSX build to Travis matrix

Also allow the Linux build to fail, for now

.travis-install-deps.sh

@@ -0,0 +1,8 @@
+#!/bin/bash
+
+if [[ $TRAVIS_OS_NAME == 'osx' ]]; then
+	brew install scons sfml boost
+else
+	sudo apt-get update -qq
+	sudo apt-get install -qq libsfml-dev libboost-dev
+fi