Merge pull request #132 from Ogeon/master

Changed to slices in tests for memstream
Unbox Request::headers.
Unbox Response::headers.
Unbox client Request::headers.
Unbox client Response::headers.
Merge pull request #134 from reem/unbox-headers

Unbox HeaderCollection
Keep up with rust
Merge pull request #136 from Valve/master

Keep up with rust
Propagate OpenSsl errors.

We lift OpenSsl errors to IoErrors, conditionally losing some information.

Without a better error abstraction, this is the best we can do without
specializing Connecter to OpenSsl.

Fixes #137
Merge pull request #138 from reem/ssl-fix

Propagate OpenSsl errors.
Add server_once method to Server