ENYO-2949:prevent overwriting problem when creating a new file of which the difference is only capital and small letters of name

Tested on OSX/Chromium 29.0.154.

* Test Case
1) Ares > select any project > select source directory > create new file > app.js
2) It shows error popup. ( Previously it overwrote the existing App.js file )

* Jira:
https://enyojs.atlassian.net/browse/ENYO-2949

Enyo-DCO-1.1-Signed-off-by: Junil Kim <logyourself@gmail.com>