Automatically validate the engines.node range using ls-engines (#1695)

* Automatically validate the engines.node range using ls-engines

Add ls-engines[1] as a dependency and use it as part of vetting
(specifically the `vet:package.json` subcommand) to ensure that the
engines.node range specified for this project is in line with all of its
dependencies. That is, if the manifest claims the package is compatible
with a Node.js version not supported by one of the (production or peer)
dependencies, it will complain.

--
1. https://www.npmjs.com/package/ls-engines

* Add exception for `jsonp` to licensee configuration

The package `jsonp` is licensed under the MIT license but does not
declare this in the project manifest. To verify the license run the
command:

    cat node_modules/jsonp/Readme.md

and look for the `## License` section.

.licensee.json

@@ -20,6 +20,7 @@
     "deep-freeze": "0.0.1",
     "filter-iterator": "0.0.1",
     "identity-function": "1.0.0",
+    "jsonp": "0.2.1",
     "shescape": "*"
   },
   "corrections": true