lib: speed up require(), phase 1

Replace calls to fs.statSync() with an internal variant that does not
create Error or Stat objects that put strain on the garbage collector.

A secondary benefit is that it improves start-up times in the debugger
because it no longer emits thousands of exception debug events.

PR-URL: https://github.com/nodejs/io.js/pull/1801


Reviewed-By: Trevor Norris <trev.norris@gmail.com>