Update XML error message text for missing libxml; update regression

output to match.

src/backend/utils/adt/xml.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/utils/adt/xml.c,v 1.40 2007/04/05 01:46:27 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/utils/adt/xml.c,v 1.41 2007/04/05 13:53:23 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -112,7 +112,9 @@ XmlOptionType xmloption;
 #define NO_XML_SUPPORT() \
 	ereport(ERROR, \
 			(errcode(ERRCODE_FEATURE_NOT_SUPPORTED), \
-			 errmsg("feature not supported;  no libxml support in this installation")))
+			 errmsg("unsupported XML feature"), \
+			 errdetail("This functionality requires libxml support."), \
+			 errhint("You need to re-compile PostgreSQL using --with-libxml.")))
 
 
 #define _textin(str) DirectFunctionCall1(textin, CStringGetDatum(str))