Add an option to HTTPSFuture to ignore Location headers

Summary: Sometimes it can be handy to get the request directly rather than following a redirect, such as a badly-implemented 404 page or a broken webserver sending data alongside a Location header.

Test Plan: Use HTTPSFuture to download data from one of said broken servers.

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, aran

Differential Revision: https://secure.phabricator.com/D6897