Python installer now requires correct Python version

Cantera/python/setup.py.in

@@ -18,7 +18,9 @@ if '@python_package@' == 'full':
           package_dir = {'MixMaster':'../../apps/MixMaster'},
           packages = ["","Cantera","Cantera.OneD",
                       "MixMaster","MixMaster.Units"],
-          package_data = {'Cantera': dataFiles})
+          package_data = {'Cantera': dataFiles},
+          ext_modules=[Extension('_spam', ['src/spam.c'])])
+
 elif '@python_package@' == 'minimal':
     setup(name="Cantera CTI File Processor",
           version="@cantera_version@",

Cantera/python/src/spam.c

@@ -0,0 +1,13 @@
+/*
+ * A trivial Python extension module introduced to force distutils to
+ * generate installation packages requiring a specific Python version.
+ */
+
+#include <Python.h>
+
+PyMODINIT_FUNC
+init_spam(void)
+{
+  Py_InitModule3("_spam", NULL,
+           "Spam, spam, spam, eggs, and spam.");
+}