cleanup the output buffer support to at least get the basic to work fixes

* python/generator.py python/libxml.c python/libxml_wrap.h:
  cleanup the output buffer support to at least get the basic
  to work
* python/tests/outbuf.py python/tests/serialize.py: fixes and
  cleanup.
* include/libxml/xmlwriter.h: cleanup
Daniel
diff --git a/python/libxml_wrap.h b/python/libxml_wrap.h
index 260e6b4..064f8a8 100644
--- a/python/libxml_wrap.h
+++ b/python/libxml_wrap.h
@@ -113,7 +113,7 @@
 } PyoutputBuffer_Object;
 
 #define PyoutputBuffer_Get(v) (((v) == Py_None) ? NULL : \
-	(((PyURI_Object *)(v))->obj))
+	(((PyoutputBuffer_Object *)(v))->obj))
 
 typedef struct {
     PyObject_HEAD
@@ -121,7 +121,7 @@
 } PyinputBuffer_Object;
 
 #define PyinputBuffer_Get(v) (((v) == Py_None) ? NULL : \
-	(((PyURI_Object *)(v))->obj))
+	(((PyinputBuffer_Object *)(v))->obj))
 
 typedef struct {
     PyObject_HEAD