This also updates all usages of the deprecated Val ctor to use
either IntervalVal, TimeVal, or DoubleVal ctors. The reason for
doing away with the old constructor is that using it with TYPE_INTERVAL
isn't strictly correct since there exists a more specific subclass,
IntervalVal, with overriden ValDescribe() method that ought to be used
to print such values in a more descriptive way.
Generally tried to make them more reliable and execute quicker.
They all now load the listen script as a trick to make sure input
sources are fully read, but also terminate() at appropriate times
so that they don't take more time than needed. They're also all
serialized with the 'comm' group so listening on a port doesn't
interfere with the communication tests.
Adjust twotables testcase - now it is faster. Shorten the output
-- because of threading, the results did not always come out in
the same order (it depends on which thread manages to sneak in
the results into the queue earlier).
