xfileinput	get input from file using XtAppAddInput: invoke with 
filename command-line argument.

Note that file input is really not an appropriate use of XtAppAddInput,
because files are defined to be ready for reading even when they don't
have new contents, so the functions registered is called continuously.  

XtAppAddInput is more appropriate for pipe or socket input.

xpipeinput	get input from pipe using XtAppAddInput: specify on 
command-line any program that prints characters to standard out.  For 
example: xpipeinput "cal 10 1989"

xworkproc	uses a work procedure to create a popup widget using idle 
time.

xstdin		gets input from pipe from stdin.
