[swift-build-dev] FYI: Change to require Package name

[Daniel Dunbar]

We currently allow:
```
let package = Package() // Note no name here
```
in a package manifest, but this turns out to be both problematic and rarely used.

I intend to move to making this required, here:
  https://github.com/apple/swift-package-manager/pull/486
but wanted to run it past the list in case anyone has an objection.

 - Daniel