gitweb: support for / as home_link.

If the webserver is configured to use gitweb even for the root directory
of the site, then my_uri is empty which leads to a non-functional home
link.  Fix that by defaulting to "/" in this case.

Signed-off-by: Martin Waitz <tali@admingilde.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

gitweb/gitweb.perl

@@ -34,7 +34,7 @@
 our $git_temp = "/tmp/gitweb";
 
 # target of the home link on top of all pages
-our $home_link = $my_uri;
+our $home_link = $my_uri || "/";
 
 # string of the home link on top of all pages
 our $home_link_str = "++GITWEB_HOME_LINK_STR++";