Travis: build matrix improvements + CPP11 build

.travis.yml

@@ -1,14 +1,4 @@
 language: cpp
-compiler:
-  - gcc
-  - clang
-os:
-  - osx
-  - linux
-env:
-  - PLATFORM=Win32
-  - PLATFORM=Win64
-  - PLATFORM=Unix
 before_install: ./util/travis/before_install.sh
 script: ./util/travis/script.sh
 sudo: required
@@ -16,14 +6,26 @@ notifications:
   email: false
 matrix:
   fast_finish: true
-  exclude:
+  include:
     - env: PLATFORM=Win32
-      compiler: clang
+      compiler: gcc
+      os: linux
     - env: PLATFORM=Win64
+      compiler: gcc
+      os: linux
+    - env: PLATFORM=Unix COMPILER=clang
       compiler: clang
-    - env: PLATFORM=Win32
-      os: osx
-    - env: PLATFORM=Win64
-      os: osx
-    - compiler: gcc
       os: osx
+    - env: PLATFORM=Unix COMPILER=g++
+      compiler: gcc
+      os: linux
+    - env: PLATFORM=Unix COMPILER=clang
+      compiler: clang
+      os: linux
+    - env: PLATFORM=Unix COMPILER=g++-6
+      compiler: gcc
+      os: linux
+addons:
+  apt:
+    sources: &sources
+      - ubuntu-toolchain-r-test