Fixing warnings with 'strict standarts' and file permission

* Delete execution permission in po and mo files.
* Passing by reference a varible and not a function. Apply coding-standards for php indentation.
* On class-wc-widget-layered-nav-filters.php I have a warning because a foreach receive a null instead an array.
![screenshot-1](https://f.cloud.github.com/assets/29663/906606/80bafb4e-fcbc-11e2-82d9-0c116c7a7978.png)