[xslt] small documentation addition

[Jason Viers <lists beanalby net>]

Attached is a small doc addition for xsltParseStylesheetDoc, which now 
mentions that the doc is kept as a reference and explains its ramifications.

Jason

--- libxslt/xslt.c.orig	2008-01-30 12:45:11.000000000 -0500
+++ libxslt/xslt.c	2008-01-30 13:07:50.000000000 -0500
@@ -6589,7 +6589,11 @@
  * xsltParseStylesheetDoc:
  * @doc:  and xmlDoc parsed XML
  *
- * parse an XSLT stylesheet building the associated structures
+ * parse an XSLT stylesheet, building the associated structures.  doc
+ * is kept as a reference within the returned stylesheet, so changes
+ * to doc after tha parsing will be reflected when the stylesheet
+ * is applied, and the doc is automatically freed when the
+ * stylesheet is closed.
  *
  * Returns a new XSLT stylesheet structure.
  */