ability to specify alt browser mapping, for chromeapp or firefox app, etc.

[mvayngrib]

when I browserify for a Chrome app, I want a slightly different mapping than I specify in the "browser" field. It would be cool if I could have an arbitrarily named field and tell browserify to use that instead of "browser", e.g.

browserify --browser=chromeapp main.js > bundle.js

and

"browser": {
  ...
},
"chromeapp": {
  ...
}

it would then default to "browser"

[mvayngrib]

oops, will open this on the node-browserify repo