clx-interface: Use a CLIM PORT to find the X server.

  * Moving towards using more CLIM and less straight X in our test
program, use FIND-PORT to open a CLX connection, and retrieve the
DISPLAY handle from the port.

  * Currently, this just adds another layer of indirection to
setting up our window, but once we have working mirrored sheets
and a CLX-GRAFT class things should simplify a bit.