Compiler crash when file casing differs

[RyanCavanaugh]

Repro consists of:

a.ts

/// <reference path="typings\c.d.ts" />

b.d.ts

declare class Promise<T> {
    x: T;
}

Typings\c.d.ts

/// <reference path="b.d.ts" />
/// <reference path="..\a.ts" />

Invoke: tc Typings\c.d.ts

Result:

Symbol.declarations, function (d) { return d.parent === currentNode.parent; } 
TypeError: Cannot read property 'parent' of undefined

[vladima]

should already be fixed