Travis CI: More fixes to really move to GCC 4.8

.travis.yml

@@ -2,12 +2,12 @@
 # http://travis-ci.org
 
 language: cpp
-compiler: gcc
 
 before_script:
   - sudo add-apt-repository --yes ppa:ubuntu-toolchain-r/test
   - sudo apt-get update -qq
-  - sudo apt-get install -qq gcc-4.8 g++-4.8 libstdc++-4.8-dev
+  - if [ "$CXX" = "g++" ]; then sudo apt-get install -qq g++-4.8 gcc-4.8 libstdc++-4.8-dev; fi
+  - if [ "$CXX" = "g++" ]; then export CXX="g++-4.8" CC="gcc-4.8"; fi
 # Travis specific tools
   - sudo apt-get install s3cmd grep zip mailutils
 # General toolchain dependencies