Add UBSAN visibility and tighten ASAN up

LSAN is still disabled for now.

.travis.yml

@@ -37,7 +37,8 @@ before_install:
       sudo apt-get install -y clang-4.0;
       export CC="clang-4.0";
       export CONFIGURE_ARGS="--enable-asan --enable-ubsan";
-      export ASAN_OPTIONS="detect_odr_violation=0,detect_leaks=0";
+      export ASAN_OPTIONS="detect_odr_violation=0,detect_leaks=0,abort_on_error=1";
+      export UBSAN_OPTIONS="halt_on_error=1,print_stacktrace=1";
     fi
   - ./autogen.sh
   - ./configure ${CONFIGURE_ARGS}