Add a control file for Travis CI.

This isn't quite as good as I'd like -- the XVFB setup doesn't support
a bunch of context creation extensions that we use, and I haven't
looked into the multiplatform stuff for doing OS X testing yet.  I
think it's a good start, though.

.travis.yml

@@ -0,0 +1,13 @@
+language: c
+compiler:
+  - gcc
+  - clang
+
+before_install:
+  - "export DISPLAY=:99.0"
+  - "/sbin/start-stop-daemon --start --quiet --pidfile /tmp/custom_xvfb_99.pid --make-pidfile --background --exec /usr/bin/Xvfb -- :99 -ac -screen 0 1280x1024x24"
+install:
+  - sudo apt-get update
+  - sudo apt-get install xutils-dev libgl1-mesa-dev libegl1-mesa-dev libgl1-mesa-dri libgles1-mesa-dev libgles2-mesa-dev
+script:
+  - ./autogen.sh && make && make check