Python fixes:
    
     * avoid Makefile
       * it calls "python"
       * it builds Python extenstion inplace
     * require and buildrequire six, as it is used in the production code
     * stop creating separete py2 and py3 dirs
       * it is not needed
       * just make sure .c file(s) get cythonized again for the latter build
     * run tests on installed modules, not on the inplace built ones
     * note that there is one more failing test on py3