Add a Config * argument to ldisc_create(), and use it in place of the global

cfg throughout ldisc.c.  Not tested other than on Mac, but all other ports
just pass &cfg as this argument for now.

[originally from svn r2250]

window.c

@@ -644,7 +644,7 @@ int WINAPI WinMain(HINSTANCE inst, HINSTANCE prev, LPSTR cmdline, int show)
     /*
      * Set up a line discipline.
      */
-    ldisc = ldisc_create(term, back, backhandle, NULL);
+    ldisc = ldisc_create(&cfg, term, back, backhandle, NULL);
 
     session_closed = FALSE;