Use fmt.Errorf instead of errors.New to avoid importing errors package
Use fmt.Errorf instead of errors.New to avoid importing errors package

We need fmt.Errorf in a couple of places, so we might as well use just one of
the error-string returning functions instead of importing a whole new package.

justinfx/pigosat,wkschwartz/pigosat,wkschwartz/pigosat,justinfx/pigosat