Really set up travis.

.travis.yml

@@ -1,8 +1,48 @@
+sudo: required
+dist: precise
 language: cpp
-compiler:
-  - clang
-  - gcc
+
+matrix:
+  include:
+    - compiler: gcc
+      addons:
+        apt:
+          sources:
+            - ubuntu-toolchain-r-test
+          packages:
+            - g++-4.9
+      env: COMPILER=g++-4.9
+    - compiler: gcc
+      addons:
+        apt:
+          sources:
+            - ubuntu-toolchain-r-test
+          packages:
+            - g++-5
+      env: COMPILER=g++-5
+    - compiler: clang
+      addons:
+        apt:
+          sources:
+            - ubuntu-toolchain-r-test
+            - llvm-toolchain-precise-3.6
+          packages:
+            - clang-3.6
+      env: COMPILER=clang++-3.6
+    - compiler: clang
+      addons:
+        apt:
+          sources:
+            - ubuntu-toolchain-r-test
+            - llvm-toolchain-precise-3.7
+          packages:
+            - clang-3.7
+      env: COMPILER=clang++-3.7
+
+before_install:
+  - sudo apt-get update -qq
+  - sudo apt-get install -y libopencv-dev
 script:
   - mkdir build
   - cd build
-  - cmake .. && make -j4 tests && ./tests/tests
+  - cmake -DCMAKE_CXX_COMPILER=$COMPILER .. && make -j4 tests && ./tests/tests