fix --with-pybindgen path handling bug

bindings/python/wscript

@@ -143,7 +143,7 @@ def configure(conf):
 
     no_net = False
     if Params.g_options.with_pybindgen:
-        conf.env['WITH_PYBINDGEN'] = Params.g_options.with_pybindgen
+        conf.env['WITH_PYBINDGEN'] = os.path.abspath(Params.g_options.with_pybindgen)
         no_net = True
 
     if Params.g_options.pybindgen_checkout: