Create less IO errors to improve efficiency of require (forwardport of #8189)

In some environment (especially when coffescript is involved) module.js
will spend a lot of time looking up nonexisting files. This is caused by the
lengthy error creation. Those errors are then immediately caught.

This change makes the lookup much faster, by avoiding the unnecessary error
creation.

module::statPath now uses the new second parameter of fs.statSync function of the
fs.js. There is a similar change for the fs.stat, adding the third parameter.

This is the forwardport of https://github.com/joyent/node/pull/8189
Two reasons, really:

1. Embedding is normally faster than chasing pointers because you're not trampling your L1 data cache.  Unlikely to matter here, though.

2. With an embedded struct, you don't have to worry about dangling or NULL pointers - the embedder is always a fixed number of bytes away.

If you look at libuv, we always use embedded structs whenever we can get away with it.