This gets tests 4 & 7 working for the most part on all unixes, with

This gets tests 4 & 7 working for the most part on all unixes, with
some minor difficuties still in the offing (some glitches remain on aix &
alpha).

The "SYNC" event handler has been decoupled into one "generator" thread
(which calls waitpid() or poll() in a loop) and a multiplicity of
"handler" threads, which actually do the work of handling various events,
as dispatched to them by the generator.