Windows fix: use mkdirp, rimraf and node-echo instead of native posix commands

This pull request fixes some Windows incompatible code (see https://github.com/meteor/windows-preview/issues/13).

Note that there is another issue (https://github.com/meteor/windows-preview/issues/5) with requiring npm modules in packages in the meteor windows preview which will still break this package. Check the issue for a temporary workaround.

A minor problem still is that `process.exit(0)` will not properly terminate MongoDB which requires a `meteor reset` after npm support has been initialized.