Added a declaration for namespace prefix.

Fixed DB schema compilation with new xsltproc.
This patch is simple hack that was introduced by Olaf Bergmann in serdev ML,
and would be revisited in the future.

doc/stylesheets/dbschema/xsl/common.xsl

@@ -1,5 +1,7 @@
 <?xml version='1.0'?>
-<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version='1.0'>
+<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
+	xmlns:db="#"
+	version='1.0'>
     
     <xsl:key name="column_id" match="column" use="@id|xml:id"/>
 

doc/stylesheets/dbschema/xsl/sql.xsl

@@ -1,5 +1,6 @@
 <?xml version='1.0'?>
 <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
+		xmlns:db="#"
                 version='1.0'
 >