Decouple X socket opening from x11_init().

Decouple X socket opening from x11_init().

Now we wait to open the socket to the X server until we've seen the
authorisation data. This prepares us to do something else with the
channel if we see different auth data, which will come up in
connection sharing.

git-svn-id: http://svn.tartarus.org/sgt/putty@10078 cda61777-01e9-0310-a592-d414129be87e