direct clients to retry rather than failing permanently.
 *  New: Expose the framed protocol in `Connection`. Previously this would
    return the application-layer protocol (HTTP/1.1 or HTTP/1.0); now it always
    returns the wire-layer protocol (HTTP/2, SPDY/3.1, or HTTP/1.1).
 *  Fix: Permit the trusted CA root to be pinned by `CertificatePinner`.
 *  Fix: Silently ignore unknown HTTP/2 settings. Previously this would cause

     *
     * OkHttpClient client = new OkHttpClient.Builder()
     *     .sslSocketFactory(sslSocketFactory, trustManager)
     *     .build();
     * ```
     *
     * ## TrustManagers on Android are Weird!
     *
     * Trust managers targeting Android must also define a method that has this signature:
     *
     * ```java
     *    @SuppressWarnings("unused")