Use fetch polyfill that does not pollute global context [DO NOT MERGE]

[gajus]

TODO:

• If this PR is a new feature, reference an issue where a consensus about the design was reached (not necessary for small changes)

#645

• Make sure all of the significant new logic is covered by tests
• Rebase your changes on master so that they can be merged easily
• Make sure all tests and linter rules pass
• Update CHANGELOG.md with your change
• Add your name and email to the AUTHORS file (optional)

[apollo-cla]

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[gajus]

I am not familiar with TypeScript, beyond the basic concept of its purpose.

The test is giving the following errors:

src/batchedNetworkInterface.ts(13,25): error TS2307: Cannot find module 'fetch-ponyfill'.
src/networkInterface.ts(5,25): error TS2307: Cannot find module 'fetch-ponyfill'.
test/batchedNetworkInterface.ts(22,25): error TS2307: Cannot find module 'fetch-ponyfill'.
test/batchedNetworkInterface.ts(60,5): error TS2450: Left-hand side of assignment expression cannot be a constant or a read-only property.
test/mocks/mockFetch.ts(1,25): error TS2307: Cannot find module 'fetch-ponyfill'.

I am assuming this is because I haven't imported type definitions for fetch-ponyfill?

[stubailo]

Yeah we might be able to somehow reuse the typings for fetch by adding some stuff to this file: https://github.com/apollostack/apollo-client/blob/master/typings.d.ts

[helfer]

Closing this, since I think it's better to track it as an issue for now. Trying to merge/close as many PRs as possible before we do a major refactor.