Check python without python bindings to get PYTHON variable

We use PYTHON variable to execute Python script, mainly to generate
documents.  Therefore it is better to always check python interpreter
even if we don't request python bindings

configure.ac

@@ -139,8 +139,9 @@ AC_PROG_MKDIR_P
 
 PKG_PROG_PKG_CONFIG([0.20])
 
+AM_PATH_PYTHON([2.7],, [:])
+
 if [test "x$request_python_bindings" != "xno"]; then
-  AM_PATH_PYTHON([2.7],, [:])
   AX_PYTHON_DEVEL([>= '2.7'])
 fi