Working in progress on fixing travis-ci error.

.travis.yml

@@ -7,10 +7,11 @@ matrix:
       addons:
         apt:
           sources:
-            - kubuntu-backports
             - ubuntu-toolchain-r-test
+            - george-edison55-precise-backports
           packages:
             - cmake
+            - cmake-data
             - gcc-4.9
             - g++-4.9
       env: COMPILER=g++-4.9

CMakeLists.txt

@@ -2,9 +2,9 @@ cmake_minimum_required(VERSION 2.8)
 
 # Check if a supported compiler is used and add c++11 flag:
 if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
-  # if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.9)
-  #   message(FATAL_ERROR "Need at least gcc 4.9 to compile.")
-  # endif()
+  if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.9)
+    message(FATAL_ERROR "Need at least gcc 4.9 to compile.")
+  endif()
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
 elseif(MSVC)
   if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS 19)