Tester enhancement

[Michael McClary <michael>]

While hacking in the URDI tester, I discovered the Tester object
was adding significant overhead to the measured time.

(A little investigation showed that over a third of the time
(about 4.2 sec) attributed to Snefru was actually overhead,
mostly in Tester and printing on Transcript.  So Snefru is only
running about factor of 600 slower in smalltalk than in C++. B-) )

So I modified Tester>>runTest to time the execution of the test
it's running and print the result as:

	Run Time = # ms

on the system transcript.

Running a null test prints as 0, 16, or 17 ms, which says
the resolution of the clock is 1/60th second (expressed as
16 or 17 ms depending on which ticks are compared) and the
remaining overhead (of the necessary 'self perform:with:')
is 0 or 1 tick.

	michael