git protocol change

The install script does not clone the nominatim repo properly when behind some firewalls. Read more here:

http://git-scm.com/book/en/Git-on-the-Server-The-Protocols

Relevant section:

"{git://} also requires firewall access to port 9418, which isn’t a standard port that corporate firewalls always allow. Behind big corporate firewalls, this obscure port is commonly blocked."