To enable SPDY proxy, use --spdy-proxy option. At time of this
writing, the only browser which supports SSL/SPDY proxy is Chrome.
Removed Location and Host header field rewrite.
Removed Downstream::force_resume_read() calls. Added missing delete
downstream in shrpx_spdy_upstream.cc. In on_stream_close_callback,
delete downstream even if response state != MSG_COMPLETE. This may
cause segmentaiton fault.
