Fix a case where an html link can be generated from unescaped input
resulting in invalid strict xhtml or potentially injected code.
An overview of a repo with a tag "1.0.0&0.0.1" would previously result
in an unescaped ampersand in the link body.
Signed-off-by: Andreas Brauchli <a.brauchli@elementarea.net> Acked-by: Jakub Narębski <jnareb@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>