v37: Change up how download/restore works a little

* Try to load the package after downloading/restoring. Previously
  that was done too early in the process.
* make previous verbose output debug output
* report a typed error instead of a string from listPackage so it can
  be asserted to provide a nicer error.
* Catch go get errors that say there are no go files found. See code
  comment as to why.
* do *all* downloading during download phase.