Add git_url subroutine, which does what git_param did before commit a2f3db2f5de2a3667b0e038aa65e3e097e642e7d, and is used to quote full
URLs, currently only $home_link.
Signed-off-by: Jakub Narebski <jnareb@gmail.com> Signed-off-by: Junio C Hamano <junkio@cox.net>