npm: upgrade to v1.4.8

* Check SHA before using files from cache
* adduser: allow change of the saved password
* Make `npm install` respect `config.unicode`
* Fix lifecycle to pass `Infinity` for config env value
* Don't return 0 exit code on invalid command
* cache: Handle 404s and other HTTP errors as errors
* bump tap dep, make tests stderr a bit quieter
* Resolve ~ in path configs to env.HOME
* Include npm version in default user-agent conf
* npm init: Use ISC as default license, use save-prefix for deps
* Many test and doc fixes