Now trying clang 3.5

cmake/travis_before_install_linux.sh

 sudo add-apt-repository -y ppa:zoogie/sdl2-snapshots
 sudo add-apt-repository -y ppa:ubuntu-toolchain-r/test
 sudo add-apt-repository -y ppa:kalakris/cmake
-sudo add-apt-repository -y ppa:h-rayflood/llvm
+sudo add-apt-repository -y 'deb http://llvm.org/apt/precise/ llvm-toolchain-precise-3.5 main'
 sudo apt-get -qq -y update
 

cmake/travis_install_linux.sh

 if [ "$CC" = "gcc" ]; then sudo apt-get install gcc-4.8; fi
 if [ "$CXX" = "g++" ]; then sudo apt-get install g++-4.8; fi
 
-if [ "$CXX" = "clang++" ]; then sudo apt-get install --allow-unauthenticated -qq clang-3.4; fi
+if [ "$CXX" = "clang++" ]; then sudo apt-get install clang-3.5; fi
 

cmake/travis_script_linux.sh

 if [ "$CC" = "gcc" ]; then export CC="gcc-4.8"; fi
 if [ "$CXX" = "g++" ]; then export CXX="g++-4.8"; fi
 
-if [ "$CXX" = "clang++" ]; then export CXX="clang++-3.4"; fi
+if [ "$CXX" = "clang++" ]; then export CXX="clang++-3.5"; fi
 
 mkdir build && cd build && cmake .. && make -j 4 && make check