module: use UNC paths when loading native addons

When using require to load a native addon the path must be converted
into a long path, otherwise the addon will fail to be loaded on
windows if the path is longer than 260 characters.

PR-URL: https://github.com/nodejs/node/pull/2965


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Benjamin Gruenbaum <inglor@gmail.com>