Specialized overload signature inheritance broken

[csnover]

In the current release compiler, the following works and compiles without errors:

interface A {
  (key:string):void;
}

interface B extends A {
  (key:'foo'):string;
}

In the new compiler, an error:

testcase.ts(6,3): Specialized overload signature is not assignable to any non-specialized signature.

[csnover]

That error is fixed but the compiler still is not inheriting the signature correctly:

interface A {
  (key:string):void;
}

interface B extends A {
  (key:'foo'):string;
}

var b:B;

b('foo').charAt(0); // Error: Property 'charAt' does not exist on type 'void'.

[RyanCavanaugh]

Logged #345