Avoid show confusing lines in gen/bundle/main.js that throws error

[kevinkassimo]

Avoid show confusing lines in gen/bundle/main.js that throws error.
Also uses as_ref avoid some unneeded clones.

For a file bad_import.ts:

import "non-existent.txt";

Run deno bad_import.ts:
Before:

gen/bundle/main.js:4339:17
          return new DenoError(kind, base.error());

NotFound: Cannot resolve module "non-existent.txt" from "/Users/kevinqian/Desktop/Programming/Deno/test/bad_import.ts"
    at DenoError (deno/js/errors.ts:19:5)
    at maybeError (deno/js/errors.ts:38:12)
    at maybeThrowError (deno/js/errors.ts:26:15)
    at sendSync (deno/js/dispatch.ts:67:5)
    at codeFetch (deno/js/os.ts:46:19)
    at resolveModule (deno/js/compiler.ts:357:38)
    at moduleNames.map.name (deno/js/compiler.ts:519:31)
    at resolveModuleNames (deno/js/compiler.ts:511:24)
    at compilerHost.resolveModuleNames (deno/third_party/node_modules/typescript/lib/typescript.js:32750:71)
    at resolveModuleNamesWorker (deno/third_party/node_modules/typescript/lib/typescript.js:20688:69)

After:

NotFound: Cannot resolve module "non-existent.txt" from "/Users/kevinqian/Desktop/Programming/Deno/test/bad_import.ts"
    at DenoError (deno/js/errors.ts:19:5)
    at maybeError (deno/js/errors.ts:38:12)
    at maybeThrowError (deno/js/errors.ts:26:15)
    at sendSync (deno/js/dispatch.ts:67:5)
    at codeFetch (deno/js/os.ts:46:19)
    at resolveModule (deno/js/compiler.ts:357:38)
    at moduleNames.map.name (deno/js/compiler.ts:519:31)
    at resolveModuleNames (deno/js/compiler.ts:511:24)
    at compilerHost.resolveModuleNames (deno/third_party/node_modules/typescript/lib/typescript.js:32750:71)
    at resolveModuleNamesWorker (deno/third_party/node_modules/typescript/lib/typescript.js:20688:69)

[ry]

Cool thanks for the clean up. I’m not sure if this is the best herutistics but I think we just have to iterate on it in order to improve stack traces.

LGTM