Shim is injected for global type name when local type of same name exists

[dsherret]

The following should stay as-is because there exists a local Response type:

interface Response {}

function test(r: Response) {}

But instead the following happens:

import * as denoShim from "deno.ns";

interface Response {}

function test(r: denoShim.Response) {}

[zandaqo]

Similar situation with code targeting browsers: usage of Response/Request triggers shimming deno.ns.

[dsherret]

@zandaqo will discuss that one in #37.