install alt compilers

.travis.yml

@@ -1,5 +1,24 @@
 language: c
 compiler: clang
+
+before_install:
+# g++4.8.1
+- if [ "$CXX" == "g++" ]; then sudo add-apt-repository -y ppa:ubuntu-toolchain-r/test; fi
+
+# clang 3.4
+- if [ "$CXX" == "clang++" ]; then sudo add-apt-repository -y ppa:h-rayflood/llvm; fi
+
+- sudo apt-get update -qq
+
+install:
+# g++4.8.1
+- if [ "$CXX" = "g++" ]; then sudo apt-get install -qq g++-4.8; fi
+- if [ "$CXX" = "g++" ]; then export CXX="g++-4.8"; fi
+
+# clang 3.4
+- if [ "$CXX" == "clang++" ]; then sudo apt-get install --allow-unauthenticated -qq clang-3.4; fi
+- if [ "$CXX" == "clang++" ]; then export CXX="clang++-3.4"; fi
+
 before_script: "bash -c Installation/travisCI/before_script.sh"
 script: "bash -c Installation/travisCI/script.sh"
 branches: