test: verify that stream.destroy() throws err
test: PUSH and trailing headers
ispdy: voip mode should be set on out_stream_ too

Signed-off-by: Fedor Indutny <fedor@indutny.com>
Added opaque_id property to ISPDY.

Users of ISPDY can use this property to distinguish connections and
choose to ignore connection errors on an old connection if a new
connection has already been established.