Clarified usage of node-style function wrappers
Clarified usage of node-style function wrappers

- Swapped out invalid `http.get` example in `nodefn.apply` for a
variation on the example in `nodefn.call`.
- Added a note to clarify event emitters do not work with the existing
`when/node/function` api.

stevage/when,caporta/when,tkirda/when,anthonyvia/when,frank-weindel/when,anthonyvia/when,DJDNS/when.js,SourcePointUSA/when,ning-github/when,tkirda/when,mlennon3/when,ning-github/when,SourcePointUSA/when,caporta/when,petkaantonov/when,frank-weindel/when,stevage/when,mlennon3/when