Travis: Force GCC version 4.7

.travis.yml

@@ -33,6 +33,8 @@ before_install:
     - export NLS=false
     - export CXX11=true
 
+    - if [ "$CXX" == "g++" ]; then export CXX=g++-4.7; fi
+
     - if [ "$BUILD" == "-O2" ]; then export STRICT_COMPILATION=false; fi
     - if [ "$BUILD" == "-O2" ]; then export EXTRA_FLAGS_RELEASE=""; fi
     - if [ "$BUILD" == "-O2" ]; then export WML_TEST_TIME=15; fi
@@ -51,7 +53,7 @@ before_install:
 
 install:
     - travis_wait sudo apt-get update -qq
-    - travis_wait sudo apt-get install -qq libboost-filesystem-dev libboost-iostreams-dev libboost-random-dev libboost-program-options-dev libboost-regex-dev libboost-system-dev libboost-test-dev libboost-locale-dev libboost-thread-dev libcairo2-dev libfribidi-dev libpango1.0-dev libsdl-image1.2-dev libsdl-mixer1.2-dev libsdl-net1.2-dev libsdl-ttf2.0-dev libsdl2-image-dev libsdl2-mixer-dev libsdl2-net-dev libsdl2-ttf-dev gdb moreutils scons xvfb
+    - travis_wait sudo apt-get install -qq libboost-filesystem-dev libboost-iostreams-dev libboost-random-dev libboost-program-options-dev libboost-regex-dev libboost-system-dev libboost-test-dev libboost-locale-dev libboost-thread-dev libcairo2-dev libfribidi-dev libpango1.0-dev libsdl-image1.2-dev libsdl-mixer1.2-dev libsdl-net1.2-dev libsdl-ttf2.0-dev libsdl2-image-dev libsdl2-mixer-dev libsdl2-net-dev libsdl2-ttf-dev gdb moreutils scons xvfb g++-4.7
 
 script: 
     - ./utils/travis/check_utf8.sh