Attempt to run travis-ci tests against multiple versions of tmux

.travis.yml

@@ -1,6 +1,16 @@
-language: bash
+language: c
 script: make test
+env:
+  - TMUX_VERSION="1.6"
+  - TMUX_VERSION="1.7"
+  - TMUX_VERSION="1.8"
+  - TMUX_VERSION="1.9a"
 before_install:
-  - sudo add-apt-repository -y ppa:kalakris/tmux
   - sudo apt-get update
-  - sudo apt-get install -y bc tmux
+  - sudo apt-get install -y build-essential libevent-dev libncurses5-dev
+  - wget http://downloads.sourceforge.net/tmux/tmux-${TMUX_VERSION}.tar.gz
+  - tar -zxf tmux-${TMUX_VERSION}.tar.gz
+  - cd tmux-${TMUX_VERSION}
+  - ./configure && make && sudo make install
+  - cd ..
+  - sudo apt-get install -y bc