Don't write update requests to the UI pipe when there is no UI; it will fill and block.  In fact, don't open the UI pipe at all.
Don't install a SIGINT handler for batch mode, since the ^C handling was depending on the gtk mainloop


git-svn-id: https://svn.xiph.org/trunk/postfish@18784 0101bb08-14d6-0310-b084-bc0e0c8e3800