Add authentication.

Other code fixing:
- Fixed bugs in get32.
- Fix code for parsing display string (as a new function).
- Fix code for connecting to X server. The old code only work
  if the server is listening to TCP port, otherwise it doesn't
  work (at least in my PC).

R=nigeltao_golang, rsc, jhh
CC=golang-dev
https://golang.org/cl/183111