podwrapper: guestunmount is a libguestfs page, don't link it to he.net.

Cherry picked from commit bd30d3a61c
and commit 0087cf2531.

Note that libguestfs 1.20 does not use guestunmount.

podwrapper.pl.in

@@ -447,6 +447,7 @@ SUBHTML: {
         return 1 if /^libguestf/;
         return 1 if /^guestf/;
         return 1 if /^guestmount/;
+        return 1 if /^guestunmount/;
         return 1 if /^hivex/;
         return 1 if /^febootstrap/;
         return 1 if /^supermin/;