Fix travis for Linux build

Several issues was detected with linux build:
- travis_wait raise timeout
- --jobs=2 sometimes fails
- add flag BOOST_NO_CXX11_SCOPED_ENUMS to fix compilation with old boost filesystme
- add missing tool xmllint

.travis-install-deps.sh

@@ -7,5 +7,5 @@ if [[ $TRAVIS_OS_NAME == 'osx' ]]; then
 	brew install scons sfml
 else
 	sudo apt-get update -qq
-	sudo apt-get install -qq libsfml-dev libboost-dev libboost-filesystem-dev libboost-thread-dev
+	sudo apt-get install -qq libsfml-dev libboost-dev libboost-filesystem-dev libboost-thread-dev libxml2-utils
 fi