fs: use `kMaxLength` from binding

This allows `graceful-fs` to evaluate `fs` source
without access to internals.

This is a temporary workaround that makes npm work.

See: https://github.com/isaacs/node-graceful-fs/issues/41
Fixes: https://github.com/nodejs/io.js/issues/1898
PR-URL: https://github.com/nodejs/io.js/pull/1903


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>