[Spec] Hiding of call/construct signatures

[mhegazy]

interface Base2 { 
   (x: number): number;
}
interface I2 extends Base2 {
   (x: number): string;  // error because base returns non-void
}

This code is illegal in 1.0 because call signature in I2 hides one in Base2. We've discussed that that this restriction should be relaxed as it covers very limited surface

[sophiajt]

Just need to update the spec to reflect that signatures never hide each other.

[RyanCavanaugh]

Would be good to understand why this is desirable?