Avoid a 301 permanent redirect.

Part of SF patch #773007.

Doc/lib/libgettext.tex

@@ -442,7 +442,7 @@ The \program{pygettext}\footnote{Fran\c cois Pinard has
 written a program called
 \program{xpot} which does a similar job.  It is available as part of
 his \program{po-utils} package at
-\url{http://www.iro.umontreal.ca/contrib/po-utils/HTML}.} program
+\url{http://www.iro.umontreal.ca/contrib/po-utils/HTML/}.} program
 scans all your Python source code looking for the strings you
 previously marked as translatable.  It is similar to the GNU
 \program{gettext} program except that it understands all the