Add support for per-file directive overrides.

JSHint has added support for overrides within .jshintrc file, as per jshint/jshint#1401.
Additional routine within the config loading procedure attempts to match this behaviour.
Unbroken the hasOwnProperty.

Code still worked, as none of Object's default prototype bits are enumerable, but it would've broken if anything was added to it.
Merge pull request #53 from D1SoveR/master

Add support for per-file directive overrides.