Testing on more compilers to see whether the CMake stuff works

CMake should fail on the gcc-4.8 build.

.travis.yml

@@ -4,16 +4,20 @@ dist: trusty
 language: cpp
 
 env:
+  - C_COMPILER=gcc-4.8 CXX_COMPILER=g++-4.8
+  - C_COMPILER=gcc-4.9 CXX_COMPILER=g++-4.9
   - C_COMPILER=gcc-5 CXX_COMPILER=g++-5
+  - C_COMPILER=clang-3.5 CXX_COMPILER=clang++-3.5
   - C_COMPILER=clang-3.8 CXX_COMPILER=clang++-3.8
 
 before_install:
   - sudo add-apt-repository ppa:ubuntu-toolchain-r/test -y
   - wget -O - http://llvm.org/apt/llvm-snapshot.gpg.key | sudo apt-key add -
+  - echo "deb http://llvm.org/apt/trusty/ llvm-toolchain-trusty-3.5 main" | sudo tee -a /etc/apt/sources.list
   - echo "deb http://llvm.org/apt/trusty/ llvm-toolchain-trusty-3.8 main" | sudo tee -a /etc/apt/sources.list
   - sudo apt-get update -q
-  - sudo apt-get install gcc-5 g++-5 -y
-  - sudo apt-get install clang-3.8 -y
+  - sudo apt-get install g++-4.8 g++-4.9 gcc-5 g++-5 -y
+  - sudo apt-get install clang-3.5 clang-3.8 -y
   - sudo apt-get install libboost-all-dev libeigen3-dev libopencv-dev -y
 
 before_script: