ENH: git clone always through https to pass restrictive firewalls

In case of restrictive (corporate) firewalls, "git clone git://..." does not work and the linux script fails, while "git clone https://..." works, provided that the environment variable https_proxy is properly set. In case the firewall is not an issue, no harm is done.
Merge pull request #3 from emanuele/git-clone-restrictive-fw

ENH: git clone always through https to pass restrictive firewalls