travis: build for osx and avahi

.travis.yml

@@ -10,17 +10,30 @@ sudo: required
 dist: trusty
 
 language: cpp
-compiler: gcc
+
+matrix:
+  include:
+    - os: linux
+      compiler: gcc
+      env: PYTHON_EXECUTABLE=/usr/bin/python PYTHON3_EXECUTABLE=/usr/bin/python3
+    - os: osx
+      compiler: clang
+      env: PYTHON_EXECUTABLE=/usr/local/bin/python2 PYTHON3_EXECUTABLE=/usr/local/bin/python3
 
 env:
   global:
     - INSTALL_PREFIX=/usr/local
-    - SOAPY_SDR_BRANCH=master
-  matrix:
-    - BUILD_TYPE=Debug
     - BUILD_TYPE=Release
 
+# whitelist
+branches:
+  only:
+    - master
+    - maint
+
 install:
+  - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then sudo apt-get install -qq libavahi-client-dev; fi;
+
   # install SoapySDR from source
   - git clone https://github.com/pothosware/SoapySDR.git
   - pushd SoapySDR