Use www subdomain by default (when there is no special subdomain in use

Currently, if no subdomain is going to be used (e.g., as a result of an OG group or what have you), all links that are generated (such as create content, admin, nodes without groups, etc.) have no subdomain. Those who have a wildcard SSL certificate would rather use the www subdomain by default since their one wildcard SSL certificate can then take care of all URIs, including all those non subdomain URIs.

I'm submitting this patch thinking that either:

a) The subdomain maintainer would rather have www be the default in which case this is good to go
b) The subdomain maintainer would rather have this be an option, in which case this needs more work

Thanks for the awesome module.