travis.yml: Add OS X testbot.

.travis.yml

@@ -1,7 +1,15 @@
+os:
+  - linux
+  - osx
+
 sudo: false
 
 language: c
 
+install:
+  - if [ "$TRAVIS_OS_NAME" == "osx" ]; then brew update > /dev/null; fi
+  - if [ "$TRAVIS_OS_NAME" == "osx" ]; then brew install openssl libidn rtmpdump libssh2 c-ares libmetalink libressl nghttp2; fi
+
 before_script:
   - ./buildconf