travis: set Python when building

.travis.yml

@@ -5,7 +5,6 @@ env:
     - CTEST_PARALLEL_LEVEL=4
     - CTEST_OUTPUT_ON_FAILURE=1
     - CXX_FLAGS_DEBUG="-O1"
-    - BUILD_PYTHON_INTERFACE=ON
     - MAKEFLAGS="-j2"
 
 cache:
@@ -79,11 +78,13 @@ before_install:
 
 script:
   # Create build directory
+  - which python
+  - which python2
   - mkdir build
   - cd build
 
   # Configure
-  - cmake -DCMAKE_BUILD_TYPE=$BUILD_TYPE -DCMAKE_CXX_FLAGS=-w -DCMAKE_CXX_FLAGS_DEBUG=${CXX_FLAGS_DEBUG} -DBUILD_PYTHON_INTERFACE=${BUILD_PYTHON_INTERFACE} ..
+  - cmake -DCMAKE_BUILD_TYPE=$BUILD_TYPE -DCMAKE_CXX_FLAGS=-w -DCMAKE_CXX_FLAGS_DEBUG=${CXX_FLAGS_DEBUG} -DPYTHON_EXECUTABLE=$(which python2) ..
 
   # Build
   - make