Allow building without Python

configure.ac

diff --git a/configure.ac b/configure.ac
index d07ff30..0fd1364 100644
--- a/configure.ac
+++ b/configure.ac
@@ -147,9 +147,10 @@
             [build_cython=false],
             [build_cython=true])
 if test "$build_cython" = "true"; then
-            AM_PATH_PYTHON(2.3)
-            AC_PROG_CYTHON(0.17.0)
-            CYTHON_PYTHON
+            AC_PROG_CYTHON([0.17.0])
+            if [test "x$CYTHON" != "xfalse"]; then
+              AM_PATH_PYTHON([2.3], [CYTHON_PYTHON])
+            fi
 else
             CYTHON=false
 fi