FileHelpers: Tolerates transient IO errors

* Uses [Enterprise Library](http://msdn.microsoft.com/library/cc467894.aspx) for "retry policy".
* Routes all File IO read/write calls to helper.
* Fixes CoffeeScript, SCSS and LESS compilation-<br>   related issues.
* Fixes TypeScript crashing issues.
* Fixes tests.
* Other minor fixes.
* Targeting #871, #887, #890, #897, #868 & #904.

More details can be found at #871.

Special thanks to @SLaks for all the tips & tricks :+1: :smile: