Fixed race conditions for FileEngine
Merge pull request #1617 from davidsteinsland/master

Fixed race conditions for FileEngine.

Using file_exists() and unlink() together does not ensure atomic results.
Add coding standards ignore comments to FileEngine

We normally disallow error supression but it is the only way to
atomically delete files.
Remove last yoda conditions as per coding standards guidelines.
Merge pull request #1618 from dereuromark/master-cs

Remove last yoda conditions as per coding standards guidelines.