Description:

The improvements are meant to normalize behavior across different
platforms and environments, and to make filesystem access more
resilient to errors.

Improvements over fs module:
- Queues up `open` and `readdir` calls, and retries them once
something closes if there is an EMFILE error from too many file
descriptors.
- fixes `lchmod` for Node versions prior to 0.6.2.
- implements `fs.lutimes` if possible. Otherwise it becomes a noop.
- ignores `EINVAL` and `EPERM` errors in `chown`, `fchown` or `lchown`
if the user isn't root.
- makes `lchmod` and `lchown` become noops, if not available.
- retries reading a file if `read` results in EAGAIN error.