Add support for Travis CI

Makefile

@@ -1,3 +1,5 @@
+PATH := ./redis-git/src:${PATH}
+
 define REDIS1_CONF
 daemonize yes
 port 6379
@@ -254,4 +256,8 @@ release:
 	mvn release:perform
 	make stop
 
+travis-install:
+	[ ! -e redis-git ] && git clone https://github.com/antirez/redis.git redis-git || true
+	make -C redis-git -j4
+
 .PHONY: test