module: reduce syscalls during require search
module: reduce syscalls during require search

require() now checks that the path exists before searching
further in it.

PR-URL: https://github.com/nodejs/io.js/pull/1920
Reviewed-By: Isaac Z. Schlueter <042dc4512fa3d391c5170cf3aa61e6a638f84342@izs.me>
Reviewed-By: Trevor Norris <9cb5491eb5770dd8e0bf77a8a0335abf5f0488c5@gmail.com>
Reviewed-By: Chris Dickinson <38a75c4c4f5646d63b752460df745c5b937b7e58@gmail.com>
Reviewed-By: Jeremiah Senkpiel <f1782d15e31ad502ea2c097c21cc235811d0cb7c@rocketmail.com>

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node