ruby: message buffer, timer table: significant changes

ruby: message buffer, timer table: significant changes

This patch changes MessageBuffer and TimerTable, two structures used for
buffering messages by components in ruby.  These structures would no longer
maintain pointers to clock objects.  Functions in these structures have been
changed to take as input current time in Tick.  Similarly, these structures
will not operate on Cycle valued latencies for different operations.  The
corresponding functions would need to be provided with these latencies by
components invoking the relevant functions.  These latencies should also be
in Ticks.

I felt the need for these changes while trying to speed up ruby.  The ultimate
aim is to eliminate Consumer class and replace it with an EventManager object in
the MessageBuffer and TimerTable classes.  This object would be used for
scheduling events.  The event itself would contain information on the object and
function to be invoked.

In hindsight, it seems I should have done this while I was moving away from use
of a single global clock in the memory system.  That change led to introduction
of clock objects that replaced the global clock object.  It never crossed my
mind that having clock object pointers is not a good design.  And now I really
don't like the fact that we have separate consumer, receiver and sender
pointers in message buffers.