Force protocol for grabbing dependencies. Usage: rebar get-deps force_pr...

Added this feature because from work I cannot access git uri:s outside of the intranet, and editing the configuration files by hand sort of sucks. 

This forces rebar to use ssh, http or https by adding force_protocol=https when using get-deps. 

It would'nt be hard to add support for the other CVS:s.

Let me know what you think!