#140 optionally ignore umask

[Scott Venier]

Sometimes corporate/project policy dictates that all packages should be group writable. But some users don't follow the policy and set their umask too restrictively. It would be nice if there was a vesta.cfg option to force vcheckout to use some specific umask instead of the user's current one.

Yes, it could be overridden in a ~/vesta.cfg, but this would at least take care of the accidental cases.