Fix bugs in Hixie-76 implementation

This is the first commit which actually works with QtWebKit 4.7 and
other Hixie-76/HyBi-00 implementations!

- Hixie-76 requires a (minimal) footer on each frame, so
  createFrameHeader needed to change to createFrameHeaderFooter
- Send any body response immediately when upgrading a connection, so the
  response doesn't get mixed up with the traffic for the piggybacked
  connection
- Fix some subtle bugs in Hixie-76 state machine