Config option to force git connections over HTTPS

commit 94ba323ae79ee4f2d7593f2544567c9c2dbf5700
Author: Jay Proulx <jason.proulx@pollensoft.com>
Date:   Fri May 31 14:13:38 2013 -0400

    Add a config / environment switch to force bower to connect to git via HTTPS when required.
    
    Some users (behind firewalls) can't use git://<gitserv>, and instead need to use https://<gitserv>