Convert only remaining uses of fprintf(stderr, ...) in xtrs to use the
functions in error.c instead.

Upstream may prefer to simply migrate an error from XOpenDisplay() to
fatal(); my approach preserves the unique exit status of this situation.

-- Branden Robinson, 2017-04-17T01:43:21-0400
--- a/trs_xinterface.c
+++ b/trs_xinterface.c
@@ -255,7 +255,7 @@
   (void) XrmGetResource(command_db, option, "Xtrs.Display", &type, &value);
   /* open display */
   if ( (display = XOpenDisplay (value.addr)) == NULL) {
-    fprintf(stderr, "Unable to open display.");
+    error("unable to open display");
     exit(-1);
   }
 
--- a/main.c
+++ b/main.c
@@ -119,8 +119,7 @@
 
     argc = trs_parse_command_line(argc, argv, &debug);
     if (argc > 1) {
-      fprintf(stderr, "%s: erroneous argument %s\n", program_name, argv[1]);
-      exit(1);
+      fatal("erroneous argument \"%s\"", argv[1]);
     }
     mem_init();
     trs_screen_init();