function consolidation when writing to xmlBuffer. Return error condition

* xmlIO.c xmlwriter.c: function consolidation when writing to xmlBuffer.
  Return error condition not len if xmlwriter fails writing to buffer.
diff --git a/xmlwriter.c b/xmlwriter.c
index 25e45fa..5911347 100644
--- a/xmlwriter.c
+++ b/xmlwriter.c
@@ -99,9 +99,6 @@
 static void xmlFreeTextWriterNsStackEntry(xmlLinkPtr lk);
 static int xmlCmpTextWriterNsStackEntry(const void *data0,
                                         const void *data1);
-static int xmlTextWriterWriteMemCallback(void *context,
-                                         const xmlChar * str, int len);
-static int xmlTextWriterCloseMemCallback(void *context);
 static int xmlTextWriterWriteDocCallback(void *context,
                                          const xmlChar * str, int len);
 static int xmlTextWriterCloseDocCallback(void *context);
@@ -275,11 +272,8 @@
     xmlOutputBufferPtr out;
 
 /*::todo handle compression */
-    out = xmlOutputBufferCreateIO((xmlOutputWriteCallback)
-                                  xmlTextWriterWriteMemCallback,
-                                  (xmlOutputCloseCallback)
-                                  xmlTextWriterCloseMemCallback,
-                                  (void *) buf, NULL);
+    out = xmlOutputBufferCreateBuffer(buf, NULL);
+
     if (out == NULL) {
         xmlWriterErrMsg(NULL, XML_ERR_NO_MEMORY,
                         "xmlNewTextWriterMemory : out of memory!\n");