Added Travis Integration

This gives us automated testing of building on linux, with each commit to github.com/audacity/audacity:master.  The run takes about 10 mins and runs on an AWS instance.

.travis.yml

@@ -0,0 +1,7 @@
+before_install:
+    - sudo apt-get update -qq
+    - sudo apt-get install -y libwxgtk2.8-dev
+language: cpp
+compiler:
+    - gcc
+script: ./configure && make