Don't use `process.chdir()`

Since Grunt can also be used via its API, I would suggest avoiding `process.chdir`.

One problem is if Grunt is used inside an [Express](http://expressjs.com) app as views expects `process.cwd` to be the root of the app folder.

Another problem is if I want to run several Grunt files in parallel. Spawning is expensive.

With [Bower](http://bower.io) it is possible to set the working dir with `bower.config.cwd = 'otherfolder'`. Something like that would be great with Grunt.

I'm using the Grunt API as I'm building a service that runs a repositorys Bower, Grunt etc when changes have been made in the master branch.

Start by tracing Grunt's API entry points and locating where process.chdir() is used. Define how an API-configurable working directory should behave for Express integration and parallel Grunt files; done means callers can set that directory without changing the host process's global working directory.

Written by the indexing model from the issue text.