Regenerating docs and API files

Various cleanups
* configure.in: force regeneration of APIs in my environment
* buf.c buf.h enc.h encoding.c include/libxml/tree.h
  include/libxml/xmlerror.h save.h tree.c: various comment cleanups
  pointed by apibuild
* doc/apibuild.py: added the 3 new internal headers in the excludes
* doc/libxml2-api.xml doc/libxml2-refs.xml: regenerated the API
* doc/symbols.xml: listing new entry points for 2.9.0
* doc/devhelp/*: regenerated
diff --git a/buf.c b/buf.c
index 09a1b2d..fa0c3f6 100644
--- a/buf.c
+++ b/buf.c
@@ -255,8 +255,12 @@
 }
 
 /**
+ * xmlBufGetAllocationScheme:
+ * @buf:  the buffer
  *
+ * Get the buffer allocation scheme
  *
+ * Returns the scheme or -1 in case of error
  */
 int
 xmlBufGetAllocationScheme(xmlBufPtr buf) {
@@ -1276,6 +1280,8 @@
  * xmlBufSetInputBaseCur:
  * @buf: an xmlBufPtr
  * @input: an xmlParserInputPtr
+ * @base: the base value relative to the beginning of the buffer
+ * @cur: the cur value relative to the beginning of the buffer
  *
  * Update the input to use the base and cur relative to the buffer
  * after a possible reallocation of its content