FileHelpers: Tolerates transient IO errors.

* Uses Enterprise Library for "retry policy".
* Routes all File IO read/write calls to helper.
* Fixes CoffeeScript, SCSS and LESS compilation-
  related issues.
* Fixes TypeScript crashing issues.
* Fixes tests.
* Other minor fixes.
* Targeting #871, #887, #890, #897, #868 & #904.
Merge pull request #909 from am11/transient-fault-resilient-io

FileHelpers: Tolerates transient IO errors