Ensure that all the default timers are called as functions, not an
expensive method wrapper around a variety of different functions.

Agressively avoid dictionary lookups.

Modify the dispatch scheme (Profile.trace_dispatch_*(), where * is not
'call', 'exception' or 'return') so that the callables dispatched to
are simple functions and not bound methods -- this reduces the number
of layers of Python call machinery that gets touched.

Remove a couple of duplicate imports from the "if __name__ == ..."
section.

This closes SF patch #430948.