Try to force using sage -python instead of python.

Author: mmasdeu

.travis-install.sh

@@ -5,6 +5,8 @@
 # without any warranty.
 set -e
 SAGE_IMAGE=`python2 -c "import setup; print setup.get_all_version_names('${SAGE_SERVER}index.html',${SAGE_AGE})"`
+echo "Obtaining Sage image:"
+echo $SAGE_IMAGE
 cd $HOME
 if [ ! -x SageMath/sage ] ; then
     rm -f SageMath.tar.bz2

setup.py

@@ -30,8 +30,11 @@ def readfile(filename):
 # Check the right Sage version
 class build(build_module.build):
     def run(self):
-        from sagemath.check_version import check_version
-        check_version(sage_required_version)
+        errno = os.system('sage -python -c "from sagemath.check_version import check_version; check_version(%s)"'%sage_required_version)
+        if errno != 0:
+            sys.exit(1)
+        # from sagemath.check_version import check_version
+        # check_version(sage_required_version)
         build_module.build.run(self)
 
 # For the tests