add a "no strict compilation" clang build to travis

At gfgtdf's request

.travis.yml

@@ -3,19 +3,22 @@ compiler:
     - clang
     - gcc
 env:
-    - WML_TESTS=true
-    - WML_TESTS=false
+    - WML_TESTS=true STRICT_COMPILATION=True
+    - WML_TESTS=true STRICT_COMPILATION=False
+    - WML_TESTS=false STRICT_COMPILATION=False
 matrix:
   exclude:
     - compiler: clang 
       env: WML_TESTS=false
     - compiler: gcc 
       env: WML_TESTS=true
+    - compiler: gcc
+      env: STRICT_COMPILATION=False
 install:
     - sudo apt-get update -qq
     - sudo apt-get install -qq libboost-iostreams-dev libboost-program-options-dev libboost-regex-dev libboost-system-dev libboost-test-dev libcairo2-dev libfribidi-dev libpango1.0-dev libsdl-image1.2-dev libsdl-mixer1.2-dev libsdl-net1.2-dev libsdl-ttf2.0-dev
 script: 
-    - scons cxxtool=$CXX strict=True wesnoth wesnothd campaignd test
+    - scons cxxtool=$CXX strict=$STRICT_COMPILATION wesnoth wesnothd campaignd test
     - "export DISPLAY=:99.0"
     - "sh -e /etc/init.d/xvfb start"
     - ./test_wrapper.sh