Change vncsession startup error message

We need to get to the point of starting the session script before we
consider things a success. So this can fail in many different ways, not
just the daemonization. Adjust the error message to something more
generic to reflect this.

unix/vncserver/vncsession.c

@@ -81,7 +81,7 @@ begin_daemon(void)
         /* Wait for child to finish startup */
         len = read(fds[0], buf, 1);
         if (len != 1) {
-            fprintf(stderr, "Failure daemonizing\n");
+            fprintf(stderr, "Failed to start session\n");
             _exit(EX_OSERR);
         }