V0.8.8 tls backport

[pfernie]

A backport of commits 11f8588 and c417d6d in order to support more recent native-tls to address #336. These commits include upgrading hyper to 0.12.

[otavio]

It seems to break the current API. It changes some public API and it is a problem for a 0.8.x release.

[pfernie]

True; changes related to the hyper upgrade end up having an impact on the public API here. Closing this PR as unsuitable for the 0.8 branch; I see there is a feature on master hyper011 to "ease transition", perhaps incorporating those changes will allow for this backport while maintaining compatibility.

[est31]

It seems that both hyper-tls and tokio-tls would need upgrades for a native-tls upgrade to happen. They require newer hyper though and hyper stuff is being reexported, so we can't upgrade it. Thus we'd have to find a way to backport the native-tls upgrade onto older hyper-tls and tokio-tls versions. This would be a giant endeavour and not sure whether it would work out at all.

I think it'd be best to ask @seanmonstar for a soon 0.9 reqwest release so that users don't have to use it from git (some can't because they are publishing to crates.io).