fix xsl error (although xalan doesn't complain it).

according to the spec it's not allowed to bind the same
variable twice or more within the same scope.
(<http://www.w3.org/TR/xslt#local-variables>)

Reported by:  Michael Schr�pl <Michael.Schroepl@telekurs.de>
Submitted by: Astrid Ke�ler
Reviewed by:  /me ;-)


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/APACHE_2_0_BRANCH@98215 13f79535-47bb-0310-9956-ffa450edef68