PR# 10744 Process library should use poll, select or pselect instead of try/sleep cycle

It may be a little late to change this (and maybe there is
something I am missing) but I noticed that classes such
as PROCESS_OUTPUT_LISTENER_THREAD use polling (try to
read data, then sleep for a little while if none) instead
of an event driven model (go to sleep until there is some
data to read).  Perhaps this is because such a model can't
be supported on Windows, but I expected to see use of
poll or select or pselect in the Unix implementation
classes.  I have some classes that use this method
(really part of eweasel but never delivered with it)
if you're interested.