Test php 7.0 and 7.1 on Travis

- php-7.1 set as failing for now due to one broken example (references)
- Look for php 7.1 in configure.ac.

Tools/travis-linux-install.sh

@@ -74,6 +74,11 @@ case "$SWIGLANG" in
 	"php5")
 		sudo apt-get -qq install php5-cli php5-dev
 		;;
+	"php")
+		sudo add-apt-repository -y ppa:ondrej/php
+		sudo apt-get -qq update
+		sudo apt-get -qq install php$VER-cli php$VER-dev
+		;;
 	"python")
 		sudo apt-get -qq install pep8
 		if [[ "$PY3" ]]; then