Add support for node-webkit environment.

Node-webkit allows loading with require in node's context, so just just
skip the node support if it is node-webkit.
Add check for node's style require.

When running in node-webkit, honor both require() and r.js
require.nodeRequire(). Allow entering the node branch of the code in the
latter case.
Revert "Add check for node's style require."

This reverts commit 902cd2bc79bd36ed878b9af832c7ddc83729daff.
Merge pull request #55 from busykai/master

Support text in node-webkit.